I just had a Pioneer plasma calibrated by an ISF certified technician and it made a very substantial improvement in color accuracy and image sharpness.
I looked at the list of folks offering ISF calibrations on the ISF website and it appears to be a mixture of folks who do this on the side and av/home theater businesses offering additional services.
My tech who did my TV does this on the side. He said that the most important thing is looking for someone who has a fair bit of experience doing calibrations as the training is fairly basic and you only get good with practice.
ISF has a suggested price range for various services. $400 sounds a little high to me but it could be that DLPs are more of a challenge. Also, the more inputs that are calibrated, the more it costs. I paid $300 for two inputs on my plasma.
You might want to take a look on the AVS forum where there is a sub-forum devoted to display calibration and many of the posts come from certified technicians.
http://www.avsforum.com/avs-vb/index.php Lots of good information, but the discussions can get pretty technical at times. As I recall, there is one thread where one or more posters named who they thought were good in the N.H./Maine area. That could just be mutual backscratching but it could be useful also.
Let us know how it comes out if you decide to go ahead and have your set calibrated.
Cheers.
David