Is your current setup rigged for sanke kegs currently? I'm assuming you already have CO2, regulator, gas/beer lines, shanks, and faucets?
Depending on what you want to do, you'll need new ball lock/pin lock taps for cornie kegs, the cornie kegs themselves...
If you want to add on to your current setup, add on a gas manifold to T off the gas, more gas and beer line, shanks, and faucets. ...thats it...
Figure 30 bucks a keg after shipping, replacing the o-rings, and lubing, $12 a set for taps. Lines could run around 10 bucks, shanks are like 20 each, faucets are another $3-40 depending on what you get (cobra spicket, standard faucet, shirrons, etc).