I buy SDRAM and DDR RAM all the time.
I've been paying about $4/stick for 512mb PC-133. This is new manufacture RAM from China. I often buy big lots of good pulls(and usually name brand RAM) for less than that, although I can count on some either not being good or not being "Mac Friendly." I bought some new 512mb Samsung PC-133 SO-DIMMs for about a $3 each not long ago.
1gb DDR is still running about $10/stick, but that's not a terrible price. I'm just not going to spend $80 to fill up a G5
I also can still get a lot of SDRAM, DDR, and even DDR2 as free pulls from junked computers, although often these are smaller capacity sticks. I have a huge box of RAM that I've gotten this way, and every once in a while I spend an evening sorting and bagging it by type, capacity, and speed(sometimes that can be really fun if they aren't marked explicitly and you end up Googling the per-chip specs).
RAM starts to get really pricey if you want high capacity 168 pin FPM, 72 pin SIMMs, or 30 pin SIMMs. I've been working on installing OS X 10.5 on a PowerMacintosh 8600, but one of my delays has been buying the RAM to make it happen. OWC sells 5v, 4K FPM 168 pin DIMMs with capacities of 128mb. The 8600 can take 8 of them, for a total of 1gb-what I really want to run Leopard. The problem is that paying $80 for RAM is a hard pill to swallow(especially when I only paid $25 for the computer).