Well, I think I heard a few wrong things from some previous posts, I'm going to try to clear up some things.
The PowerMac 7500/100 is faster than the 7200/120, because if its interleaving memory. The PowerMac 7200 series doesn't have interleaving DRAM, but it can support interleaving memory VRAM to acheive a 64-bit data path (one of the reasons I bought more VRAM for my PowerMac). The 7500 also costs more because of its video input/output capabilities and its removable processor.
On a completely off subject, one of the reasons I didn't get a PowerCenter 120 is because it is based on the 7200 motherboard design. It also costs much more. I got my PowerMac 7200 for a good $979. You've also mentioned RAM prices, I bought RAM for $200 + $7 shipping/handling. I bought my RAM after I got my PowerMac, in that 3 day span of time RAM prices dropped a $30. So I'm guessing that you can get RAM now for under $200.
After using my PowerMac a few days, I wish it could be faster at some tasks. Luckily, it is fast enough for now, and hopefully for a few year when I upgrade my Mac to a PPCP machine.