Old lenses for new cameras

Hi!

Im about to but a G3, and I want to know a little bit more of the lenses that I can buy. I've been told that micro lenses are more expensive than similar nikon or canon lenses, but B&H says otherwise, so I dont know if that is true.

Also, I've read that old manual lenses can work perfectly with the system and are less expensive, but I don't know which old lenses are the best for the system!

Thanks for your help!