Well, it's a bit of a vintage piece of kit (dates from Apple's pre-Intel days).
The reason for the price is evident if you look at the CPU, its a non-standard PSU, it had to be to fit into that shape.
I suspect eBay might be a good source.
To be honest though, there's not much point to hang onto pre-Intel Macs these days.... and the current versions of OS X are light years ahead of what the first non-Intel releases were.
The original poster might be better off investing in a newer Intel based mac, even if it's a second hand one.