Hi, well the captcha is free, the other expense is the coins and your time...à
The cost depend on the traffic you have, more traffic cost more coins but you make more revenues with your ads...
I am making more money with my faucets than what it cost me in coins, and i've been running them for 2 years now.
For the security, you have to always be on top of things because, it takes more and more security and you have to update/upgrade your system regularely.
Finally, in order to make money with a faucet, from my personal opinion, you got to have an ADSENSE account and put google ads on your site. If you don't have that, i think it will be almost impossible to make money with it....
Good luck
