Not as difficult as you might think, BUT... Have you got all the tools you will need already?
The front bumper will need to come off too, and probably the crossmember. Even if you know what you're doing it's several hours work. The problem is you've been quoted a labour rate that sounds like it's gonna be £100 an hour. Find a good independent mechanic for £30 an hour instead, and you'll more than halve that repair bill including the cost of the new compressor.
Check eBay for compressors too, my passat engine died but the compressor was fine, broke the car for bits and sold em all on eBay, I only got £40 for my immaculate condition compressor! You Might be lucky possibly...
Once fitted, assuming correctly, you can then get it regassed. But for the love of god, stay away from Kwik Fit(up)...