try that website for some good bargains!
Upgrade your RAM (memory) and your PC should be able to run a CD-RW or DVD-RW fine! You should be able to buy more memory and a rewriter for your budget. You already have 256, so another 256 will make it 512 which should be enough.
click here - CD rewriter £10.20
click here - DVD rewriter £23.99
click here - 512MB RAM - £32.23
click here - 256MB RAM - £19.99
NB - the memory shown above will give you an idea of the price, they may not necessarily fit your particular PC because there are many types of RAM. However, the website I recommended you should have the type of memory you require.