There is 2 things that piss me off about comp hardware:
1) when people confuse the "tower" with the "CPU" and the "Hard Drive"
2) When people get the terms "DDR" and "PC" Mixed up. Its PC3200, not DDR400. DDR400 stands for Double Data Rate 400MHz. If your ram's bus speed was really at 3200MHz, i would come over to your house right now, beat you up and steal your RAM.
Anyways, now that im done with my rant =D The brand, type, quality, and speed is what normally affects the price.
BRAND: Brand name doesn't really impact it as much as it used too. Kingston seems to have the cheapest, but i haven't really been watching the memory market lately.
TYPE: Unbuffered, Unbuffered ECC, Registered, and Registered ECC are the types you can get. ECC stands for Error Correcting Code btw, its not neccessary, but is kinda nice to have, however unbuffered ECC RAM is had to find. If you want more info, resort too google, as im tired and don't feel like explaining it any further :P Also not the subcategoried of the RAM types, which are SDRAM and RDRAM. SDRAM = Synchronous Dynamic Random Access Memory, and RDRAM = Hell if i know, i just know that it fails, don't buy it. Unbuffered has slightly more bandwidth, although it's not good with servers as it require more electrical current, thus less modules can be used on 1 motherboard. Also, there is some slight price differences btw 184-pin RAM and 200-pin RAM
QUALITY: Should be self-explanetory
SPEED: lessee, the speeds are PC2100, PC2700, PC3200, and PC4000 (or, these are the common ones anyways), and these can also be found in Dual channel kits, giving speeds such as the common DDR400. You also need to consider the timings, high performance RAM with timings of 2-2-2-5 will cost more than valueRAM with timings of 2.5-3-3-7 (my RAM
)
hope you find this useful!!