I'm not an expert but 250 looks like a deal!
If you can fix it, bam that's a $1000 computer. If you can't, I'm sure that the iMac could be sold for parts much more than $250.
I had an iMac for 2 years and the one thing that irked me was the lack of portability. I recently got an early 2008 MacBook Pro for Christmas and it's amazing! Faster than my iMac and I can take it anywhere. Just want to advise you, keep an eye for good laptop deals. I believe the MBP was $500.