If you have an old custom built machine laying around collecting dust,
considering selling the parts on Ebay. Typically, older full systems
do not sell well because it costs more to ship them than they are
worth, however the parts sell quite well. If you don’t think they will
sell well individually, consider selling them as a lot. Something is
always better than nothing and if you have no plans to use your old
system, at least get something for it.

For example, I recently sold an old Socket A motherboard, 3 Pentium 1
CPU’s, and about 5 random PC-133 memory sticks and got over $100. Not
bad for some stuff which was inevitably destined for the trash.