The park tool site is a awesome reference.
www.parktool.com
Heres my opinion of a tune up. Its something you can do yourself much better. I work in a bike shop some. I think most shops charge around 40 bucks, they clean the chain, lube it, check the breaks and shifting, check the headset for smooth action, check the tires, check to see if anything is loose. Unless the bike has a serious problem it takes about 15 minutes.