[yuriyuri]

Are you coding this site yourself or getting a company to do it?

If you are doing it by yourself you need to pay for a server and bandwidth.
Assuming you are good enough to write a site like this the only other cost is your personal time.
(Although since you are asking these questions I assume you do not have experience in doing this stuff yourself)

If you are paying a company you need to pay for everything they do too, which they will dictate prices on, so no one can tell you how much that will cost other than the company themselves.

In short $100 will not really get you anywhere.

(By the way, didn't you resign from this site the other day? lol)