Hiring a lawyer, like hiring any consultant, can be frustrating. You are asking someone you don't know to do something that seems pretty clear in your mind but which has never been done before. Every invention is different, so every patent application is different. If yours is not, then you don't need a patent for it. The price of a patent will depend on the complexity of the invention, the intended industry, the attitude of the patent office in the technology area, how well your idea complies with patent claiming traditions, etc. It can take between $3,000 and $30,000 to get an application written and filed at the United States Patent and Tradmark Office (USPTO). Most patents seem to cost between $8,000 and $11,000. If you have a large number of similar or related inventions, then that price can be less. While that kind of a range is not very helpful, we can come to an agreement in advance after discussing your goals. I can make a committment in advance to stick to a price, but that only lasts as long as you stick to the original invention.
This price to file the patent is only the beginning of a process that has many more steps. If the application is filed as a regular non-provisional utility or design patent applcation, then the next step is for a patent examiner to examine the patent, search for prior art, and issue a rejection. Almost every application is initially rejected. The effort required to overcome this rejection and perhaps later additional rejections cannot be known in advance.
The United States Patent and Trademark Office has posted a great amount of helpful information about the patent process and about differnt types of patent applications at uspto.gov. You might also want to look at epo.org and jpo.go.jp
We are each given only so much time to live. Each of us must decide for ourselves how to spend the time that we have been given. If your legal work is a nobler cause than what I am giving to now, then maybe I will do it for free. Barring that you have at least two other options. First, you can write, file, and prosecute the patent application yourself. The patent examiner will probably be pretty helpful, but your patent will probably not have the legal power of one prepared by an experienced attorney. Second, you can apply to the official USPTO Patent Pro Bono Program. This program is administered by a different nonprofit agency depending on where you live. The agency screens for income and whether your idea seems appropriate for patenting. In Denver, the agency may also help you get a business started. If you are accepted, then an experienced attorney will be assigned to your case. You are only responsible for the government fees.
A patent typically gives the owner the exclusive right to make, use, sell, and import the claimed invention in the country that grants the patent. A US patent only allows the owner to exclude others within the US. To get those rights in another country, a patent application must be applied for and granted in that other country. All of these applications in other countries must be filed shortly after the original application and yes the cost can add up. Each additional country can cost $5,000 to $20,000 just to obtain the patent. Enforcing the patent is another entirely separate cost. Consider $10,000 for each of just 20 of the 153 countries that are members of the Patent Cooperation Treaty. Now consider that many countries require that an annual fee be paid to keep the patent in force. The annuities start at a few hundred per year per country and increase over time.
You don't.
By International Patent most are referring to a process under the Patent Cooperation Treaty (PCT) administered by the World International Property Orgnaization (WIPO). WIPO has a great amount of information at wipo.int. In the 1970's representatives from many nations gathered to negotiate a world patent system, but they could not come to agreement. There is still no agreement. They settled for a world patent application system. This is a great thing for some purposes. As it stands now, you can file a patent application, have it examined by an examiner at one of a choice of different patent offices, and perhaps receive a favorable opinion from that examiner. In some cases, that decision will be honored or at least taken into consideration by some national patent offices, but the International application cannot become a patent. To receive an enforceable patent, the International application is filed at one or more national patent offices in a process called the national stage entry and then evaluated at that office. Most countries give some credence to the favorable opinion, but others completely ignore it. If you want a patent in some certain juridictions, then an International application might save costs, but for most it is a cost adding delay mechanism.
You don't.
There is a European Patent Office which receives, examines, and grants patent applications often in competition with national patent offices of Europe. As an example, you can file a patent application at the German Patent Office in Munich or at the European Patent Office in Munich or both. After the European patent application is granted, then in order to be enforced, it must be registered in a participating European country. There is a registration fee, some translation, and then an annual maintenance fee. It can be said that you are then enforcing your European patent as registered in e.g. Germany or Italy. When you do this you are enforcing it through the German or Italian courts and the German registration can be treated very differntly from the Italian registration. Germany could declare the European patent invalid, but Italy could declare it valid and award an injunction, for example. In effect, they are still treated as two different national patents.
There is no European Patent Court. This has been under discussion for over 20 years. There is a proposal to allow a European Patent to be registered as a Unitary Patent instead of being registered separately in each country. This proposal also establishes a Unified Patent Court to enforce the patent. In 2016, it seemed that the Unitary Patent and Court were just around the corner, now it is quite far away. The Unitary Patent system is part of the European Union, but the European Patent Office is not. This causes some complications but the bigger problems are first that Germany may not be willing to give up its control over enforcing patents within its borders and second that the United Kingdom is no longer a member of the European Union. Without one of these countries, the Unitary Patent system might make sense. Without both of these countries, it probably will not happen.