the first one has to be the 1972 Yamaha 250 DT2MX.
I owned and raced one as a 15 year old, and for a 15 year old in 1973 it was quite a thrill. these aren't mine, but ones just like it.
If the right one comes along, I'll buy it!
They seem to go for around $1500 US Dollars in good shape, restored.
Maybe a little more if the bike has good shocks.

