You’ve found about the best deal for Branded memory, but if you don’t mind going for none branded, then try the links below.
The reason PC133 memory is expensive is because it is very little used these days, so manufacture is limited. It was mainly used in Pentium 3 systems, but was superseded in about 2002/2003 when the Pentium 4 became more mainstream with its DDR memory.

Bill
http://www.savastore.com/productinfo/pro...207&rstrat=3106
http://www.misco.co.uk/productinformation/~64056~/512MB%20PC133%20256BIT%20DIMM.htm
http://www.rlsupplies.co.uk/products/product.asp?id=612
http://www.microdirect.co.uk/ProductInfo.aspx?ProductID=3150&GroupID=466