At Monticello, I highly recommend the cafe they have on site. They use some of the locally grown food and it is excellent. Well worth the price.
I agree with highly and I didn't think the prices were out of line.
Speaking of Monticello, it is great, you can easily spend most of a day there if you do everything.
Now on the other hand, I think Michie Tavern is over priced. The food is not that good, but I guess you're paying for the atmosphere.
While you're in the area, stop at Carter's Mountain Orchard. (You'll pass the entrance going to Monticello) They have stuff to eat, a really cute store and fresh fruit in season.
If you are in Charlottesville in a Saturday morning, The Charlottesville City Market (it's like a Farmer's Market) is awesome, look for the Mennonites selling their fresh baked goods.
In Waynesboro, Scottos Italian Restaurant has wonderful food and is VERY affordable and has huge portions.
In Staunton, The Depot Grille is a fun place, good food and won't break the bank. Also Kline's Dairy Bar & Hog Wild BBQ has THE BEST ICE CREAM ever!!!
Okay, that's all I can think of right now - I'll post most if they come to me. That part of Virginia is beautiful, have fun!