You may want to consider the Betson Imperial 3" PS/2 trackball. It's a true arcade trackball, not a PC one, but it connects directly to your PC's PS/2 port. They sell for $79, and you don't need a separate interface for them, so that makes them pretty attractive.
I have had a couple of Happ and Imperial 3" trackballs, and I honestly believe the Imperial has a better roll and feel to it.
J_K_M_A_N has a bunch of part numbers and descriptions on his site here: http://jkman999.tripod.com/Links.html
FYI... a lot of BYOAC's like the translucent trackballs for aesthetic purposes, but they are actually inferior to the cast polymer white trackballs. The white ones are quite a bit heavier and have a better roll to them because they are more dense. When I talked to their VP of Sales, I asked about the translucent trackballs. He told me that they only carry them because misinformed operators and BYOAC'ers (he frequents these boards) request them, but they don't recommend them. I would have to imagine the same goes for the Happ translucent trackballs, but I don't know for certain.