512MB. Possibly even 256MB. Why so little?
Because RAM is relatively dear right now, seeing as Siemens and Micron and Samsung et al have given up on trying to send Hynix broke. In October last year, at the height of the nastiness, RAM accounted for, on average, 1% of typical overall system cost (according to one of those count-em-up-and-make-people-pay-to-see-the-number crowds - Gartners or someone), which was the all-time low. Right now, it accounts for 6% of total system cost, and is actually selling for more than it costs to make. (Which has not been true since last winter - last summer for you downsideup types.)
Because of the price war, some manufacturers went out of business - notably Toshiba - and many companies took the opportunity to close down lines to transition them to new technology - 256Mbit chips, or DDR, or both. (Seeing as you have to close the line to update it sooner or later anyhow, you might as well do it while it's running at a loss.)
Coupled with those two factors, both of which have led to an overall decrease in production, the PC industry worldwide is in a gentle recovery from its self-inflicted post Y2K troubles now, and demand is up.
Net result: RAM is in mild shortage right now, and rather too expensive for my liking. Most of the majors have their OEMs and distributors on allocation, though still a reasonably generous quota at present, and are not selling to traders at all.
Recommendation: hold.
Just buy as much as you actually need, and wait for the price to drop again. Remember that all those idle lines which are transitioning to 256Mbit production will come back on stream before too long, which will effectively cut the cost of production by almost 50%, because it costs about the same to make any kind of chip, and if the chips are 256Mbits each instead of 128Mbits, then you're getting twice as many MB for almost the same dollar. To begin with, of course, that won't affect the price, just improve the bottom line of the early adopters, but sooner or later the net doubling of overall production capacity (same number of lines, same number of chips, but twice as many megabytes in total) will drive the market into over-supply again and the price will start to drop. How long? Three to six months is my guess.
Buy as much RAM as you need now, and get more later.
How long is PC-2100 going to be current for anyway?
BEWARE: the above applies more to SDRAM than it does to DDR, though it applies to both. DDR is cheap relative to SDRAM at present because the expected surge of Intel-based DDR systems is taking a lot longer to happen than anyone expected. SDRAM is in shorter supply than DDR. When Intel buyers finally make the DDR transition, it might push DDR prices up until the RAM industry adjusts its production mix. The longer it takes to happen, the milder the effect will be.
Oh, and if you are buying (or not buying) RAM based on my price predictions, can you put $20 each way on number 4 in the Caufield Stakes for me please.