Disclaimer: I'm not a patent attorney. I've just been involved in a minimal amount of licensing negotiations.

Outside of the costs of an attorney, there are a fairly substantial amount of fees involved just for filing the patent and having it examined. Those costs could go up if your patent qualifies for a divisional patent (multiple patentable concepts within one application).

If you obtain a patent, you will still have to pay maintenance fees to keep it. They vary depending on the size of the entity that owns the patent. There are up to three payments that are scheduled during the lifetime of the patent (3.5 years, 7.5 years, and 11.5 years - I think). They begin around $400, and they can be up to $7,500 or so for the last fee. Those figures go up if the payments are late.

Even then, you will only have a patent in the U.S. You have a short grace period to file patents in other countries. That's also expensive. There are groups in China and other countries that comb through U.S. patents so they can use any new ones with merit. There is also a computer program designed to find a way to supplant a patent or obtain a superior one based off of an existing patent.

There is no way to calculate how much it could cost to enforce a patent.

If you have an invention that could make money, there will be plenty of people who will try to steal it from you. Be careful who you disclose it to. If your patent hasn't issued, a company could file something like it and create an interference. Then they can basically outspend you in legal fees until you give in and settle.

It is extraordinarily difficult to make money as an inventor, but it isn't impossible. What I said sounds discouraging, but it's only meant as a warning. Best of luck whatever you decide to do.