Yet another newb question... What type of sandpaper abrasive is the best for using on razors? Where are you guys getting it from?

I just bought a bunch of papers from Harbor Freight, and I've been pretty happy with them. They are all Emery, 60 through 220 grit. The problem is the finest they have is 220 grit. I bought some 400 grit from Home Desperate, but it's *very* expensive, and doesn't last long at all. So I guess really what I need are some pointers to some good 400, 600, 800, and 1k grit papers. I was thinking of getting some from here... Bullet Wet-or-Dry Sandpaper 9″ x 11″: Wet-or-Dry Sandpaper 9"x11"_p Bullet Industries but it doesn't say what type of abrasive is used in the paper.

BTW, the 40 micron and 15 micron 3M films used for sharpening are *fantastic* for sanding... they cut *fast*, but they are too expensive, and the gap from their 15 micron to the next finest is too large.

Help?