You can always make a baffle out of MDF to fit 6 1/2....that way you will have a TON more choices....Its going to be hard finding something at 100 shipped, 200 sounds a little more reasonable...
Search the classifieds for used components and read about them...
i ran 6.5"s and 7"s in my mustang, not at the same time. if you wanted to spend a little more, you can go with the boston SL80's, or you can go witht he pioneer tsd-680r's, eclipse, diamond. those are all good coaxials.