I saw some 1gb memory sticks rated @<hidden> 700mhz (twice the speed of my PC3200) for not a lot more than £10 each. Unfortunately, they are not the 184 pin variety I need, but I thought well, they're more recent than mine so I should be able to upgrade my current 1/2gb RAM cheaply.

Wrong! The 1gb PC3200 sticks are over £33 each. Why?

In general, the older and slower the RAM, the more expensive it becomes (apart from the bleeding edge stuff like DDR3).

Why? Supply and demand I guess, as factories upgrade their processes to manufacture the newer RAM in volume, it gets more costly to produce the older types of RAM, for a far lower demand.