AC problem, and accessories question

Well I have a problem with my 2001 impala, sometimes the AC will work and sometimes not, if I turn on the AC sometimes the air doesnt cool like it needs freon, sometimes if I leave it on after awhile the AC will kick in and work usually on a fast acceleration. I have been told by some it may be a pressure switch, how hard is that to replace and is it expensive? Is it the likely problem? I was thinking of filling it with freon myself but dont want to spend money trying things only to find that it doesnt work.

Also, I am looking for a few acessories if anyone could help.

I am trying to find a white front license plate cover like the one here for a 2001 white impala

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7911947685&category=33640

I have searched the web and cant find one

Or as an alterative a chrome chevy license plate to put on the front of my car like the one pictured on the front of the first car on this page

http://www.impalahq.com/Car_photos/Car_photos1.html

Thanks.