I've gotten pre-cuts from Dick Blick (www.dickblick.com) and been pleased with the quality, but I'm not selling my work either, so if you go with my suggestion, get a small quantity and make your own judgement. They ship quickly and have very similar products.
I still get stuff from Light Impressions on occasion, but I know what you mean. I tried to get a small quantity of pre-cut mats second day shipping for a show recently and the shipping was as much as the items ($43) ! I got what I needed from Dick Blick in the same amount of time for half the shipping cost, from the same shipper. An alternative for some of their products might be Freestyle. I get Light Impressions crystal clear protective bags from Freestyle rather than Light Impressions Direct for convenience reasons and it works out great.