Check the owner's manual of your car; it should have a section detailing regular maintenance, major replacements you can expect, etc. If you're overdue for something and the shop says it needs doing, you can probably safely assume that you should get that done.

As to stuff that's not in there, the only way you're going to know for sure is to take it to another place or two and ask them to look it over. Tell them that another shop said you needed a lot of work done, and you want a second opinion/diagnosis. Don't tell them what the other shop wanted to do, though.

Lastly, in regards to price, shopping around makes sense if you're talking about a big bill, but if you just want to know what's ballpark-fair, repairpal.com can usually help you out.