Volkswagen Repair: A/C help!, expansion valve, freon

Question
I have a 1997 Jetta Trek (1.8L).  My car has about 220,000 miles and I have had relatively few issues w/ it.

However, lately I have been having problems w/ my A/C.  Sometimes it blows cool and other times not.  It seems to do best in city driving but on the highway it almost never blows cool.

The A/C place that I took it to told me that I will need a new compressor and expansion valve @ about $400 installed.

I would rather not put $400 into this car, do you suppose there might be another option?  And if not, how much money can I save by purchasing the parts online and having the mechanic do the install?

Thanks for your help!

Answer
Lance,

I'm not sure if you could get this repaired any cheaper, but I wonder if they've diagnosed this properly.  If your freon is low the expansion valve will freeze up. Check under the front bumper at the drivers side headlight, and see if the reciever dryer is wet or oily.  
The fitting tends to corrode and leak.

Good Luck,

Paul