I have, and have had for a long time, a 1976 Bultaco Frontera mark II 250.
My old man bought it brand new for desert racing. It sat in the shed for years, and then got a rebuild about 4 years ago. It doesn't have 4 hours on it since. Magneto is buggered. It is in immaculate condition.
I don't think it is legal for vintage racing in Australia. But it is a two stroke, air cooled, twin shock monster! Scary when it got on power band.
One of my mates is currantly doing up his old Montessa 360 so he can sell it.
Its not in the greatest of shape but it runs great and is air cooled, drum brakes and twin shocks. I think he wants about $2000.
I don't think it is legal because it is a 76 model. And I think, and I am not to sure here, that vintage mx in Australia has a cutoff date of somewhere around 74.
I don't have a clue on how much it would be worth.
I will have to consult with my old man about the price, but I am going to visit him this weekend and I will take some photos of it with my digital camera and email them to you with some thoughts on price.
The bike is located in Narrandera, 100ks west of Wagga Wagga.