That's a 1973 Yamaha DT3 250 Enduro. Fully restored samples can go for as high as $ 4,000.00 to the "right" buyer. Although not see in public that often, they are not that rare.
You sample is missing some of the more expensive and hard to find parts like the head light assembly, the tail light, rear fender, key switch, etc. In the condition shown in the pictures I would think you could get $ 400.00 - $ 500.00, maybe even $ 600.00 to the guy who does not know what he is getting into.
These were good bikes in their day however compared to today's dirt bikes and dual sport bikes, it's like night and day.
BTW, I have 2 CT-1's, 1 AT-3, 1 DT-3, and 1 Yamaha RT 400 enduro's in my own collection. They all have been restored however due to the high cost of and availability of parts, they never get ridden.
Tom
