Hi Dave,
I looked up the T35 in the "Buying and Selling Guide", published as a free insert by Classic Bike magazine here in the UK. It's four years old now, so I will leave you to make your own adjustments for inflation, but I understand that the prices it quotes were mostly supplied by insurance companies, so it might help. What it says is this:
"Another unconventional Douglas design, featuring interesting torsion bar suspension front and rear and chain final drive. Single plate clutch, four speed gearbox. Later models featured radiadraulic front forks. Rare and wonderfully eccentric British motorcycles, these are currently the most common Douglas models in the marketplace."
One wonders how it gets to be rare and the most common both at the same time!
The price is A £3000, B £2500 and C £1250.
"A" means top quality machines, but not necessarily to concourse winning standards. "B" assumes good general roadworthy order with an MOT certificate. "C" means complete and running, but in need of work to reach MOT standard. I guess if you're out there winning prizes then you can claim to being an "A".
(An MOT is the annual safety inspection that all UK vehicles over three years old have to have before they are allowed out on the roads.)
Other Douglas models in the same guide are:
80 plus. A=£3000 B=£2000 C=£1500
90 plus. A=£5000 B=£4000 C=£3000
Dragonfly A=£3000 B=£2500 C=£2000
Don't forget, all these prices are four years old and in British pounds. Hope this helps,
Stuart.