They are incredibly solid and reliable engines, I'm sure it could be a decent enough woods bike, I'm sure you could get that bike for a grand or less depending on where you live. I have a yz426 with the wr headlight/stator etc, I paid 1400 for mine in good condition. Never had any problems finding after market parts for it... Honestly the only thing you don't have plentiful options is with plastics. If you don't want blue or white, prepare to have to shop around, as the other colors; yellow and black are becoming scarce.
There is just always the risk when buying old 4 strokes that there are quite a bit of things that can be wrong with it compared to an old 2 stroke... So inspect it the best you can before you buy and make sure to take it for a spin.
Also to say something about these engines, I bought mine and it already had quite a bit of hours and I put over 12,000 miles on it while also using it as my daily to get to class the last two years and rode it hard on the trails on the weekends... Never had any issues.
Edited by fdme, November 10, 2013 - 12:52 PM.