It all depends on what kind of lenses you are cleaning, and what kind of problems (dust, fungus, haze/fog, or oily aperture blades). If just some dust, don't really worth cleaning imo. Same goes to light fungus near the side.
For a normal 50mm lens, it's quite cheap, probably $30 to 50 each. For a longer prime lens, it'll take abit more, 60 to 80. It's more expensive for zoom lenses.
I like the fast service at The Camera Workshop (Peninsula Htl), good price too (one week). The Cam.X (in the same building as TCW) does quite good job too, but takes alot longer (two to three weeks). I know some guys like the Camera Hospital, but I'd never been there. Some other shops will take this kind of jobs too: Prime Camera Center at Peninsula Plaza, Ron's Camera at Adelphi, P&G at Adelphi.
Good luck