Well if you went and bought it anywhere else, it'd be $499.00 for Samsung, so yeah, dell is a rip-off.
Start here:
http://www.pricewatch.com/
You can find SOME deals. Nothing great though. It's looking like around $200.00-220.00 per 512MB PC 800 RDRAM RIMM stick.
Remember, you gotta install this stuff in pairs, so that means $400.00-440.00 + shipping for 1 GB RAM.
I did see some 512 MB 'kits' (2 sticks of 256 MB PC-600 RDRAM) for around $120.00, but PC-600 is usually pc-800 culls clocked down, nothing you really want to depend on.
It would probably be cheaper to buy a new Motherboard and rebuild around DDR, provided your processor isn't a socket 423. IF your processor is a socket 423 the only mobo I could find that is non-RDRAM only takes standard SDRAM. I just rebuilt a socket 423 system, so I know whereof I speak.
Good luck to you! You're gonna need it.