GRC has really nice stuff and is worth checking out if you are in SE PA. You pay for nice stuff of course. Prices on ebay are high and you should just call them if you are interested in something to see what the real prices as. Mike and Ray (and Jim!) stand behind their work and will take care of you if you have any problems.
If you don't want to pay for a premium machine there are plenty of other options in the area. Pinball Gallery has a retail store right down the road and has a ton of machines in the $1-$2k range that tend to be priced fairly based on their current condition. Bill's games are all actively getting played so you can how well they are working but you are also not going to get any minty HUOs from him. Bill stands behind his machines as well and is a great guy who isn't pushy about sales and just likes to have more people playing pinball.
Personally, I like having options and I'm glad these guys are all in the business. Buying on ebay and craiglist is OK for certain people, but if you just want someone to stand behind a machine and help you fix it when it eventually breaks, the local retail pinball shop is by far the best choice.
-Jay