I know it might vary depending of kind of product.
I'm planning to register a very unique Intellectual Property internet service patent
Let's suppose the world doesn't have search engine yet, and I am going to register my new product (google)!
what am I expected to pay and how much?
You're probably going to want a patent attorney to handle your business. If you're filing for a provisional patent, you're looking at 3-5K. A provisional application will secure a filing date and then you'll have a year to convert your provisional application into a full-fledged application. If you're filing for a full-fledged application from the onset, it could be around 10K or more, depending on how much work is required by the lawyer. A good idea would be for one lawyer to draft the application and then spend 1-2K for another lawyer to give you his opinion before you actually file.
In a nutshell, the cost is a function of the work to be done and therefore the more upfront work you put in yourself, the less time an attorney will take. The figures I gave are based on my own experience and I'm sure the actual cost for your patent will be different.
If this is for USA and you can claim you are a SMALL entity then you can create your own provisional patent application (do not need an attorney) and pay only $75 in fees. Then within 2 years you must submit a non-provisional patent via an attorney.
Or you could do us all a favor and quit supporting a broken scheme. If you build it, build it well, and execute well on it, you don't need the patent and you can be wildly successful.
Chances are what you think is highly unique isn't, or if it is, there are other ways to achieve the same goal. $10K is money that is probably better spent building the thing you are trying to protect.