I went the other way round, putting drops on a hybrid. Complete new drive train (brake/shifters, chainset, cassette, derailleurs and chain) bars, tape and new inner/outer cables. It was a lot of work and cost me around £200 - i was lucky though and bought a lot of the gear in one hit from the classifieds on here....
Depending on what speed you will be looking at, I have a set of flat bar suitable brake/gear shifters (trigger style) going.... also an 8 speed triple derailleur (front) and rear derailleur too....