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
