Not hard to find older SAM 440ep boards for a couple hundred bucks.
While the low end of OS4 machines, I still find mine extremely enjoyable and capable. Though my requirements and expectations of it are admittedly low, I still find it fun for what I use it for - running a BBS, a bit of web browsing, and coding.
I still run mine in barebones fashion (no add on graphics card) and find it very snappy and fun to use. The addition of a couple SSD's about a year ago give me 10 second or so boot times, even on admittedly slow hardware by todays standards.