Parkers has a van valuation bit in the printed version and you can get the same online but you have to pay a few quid for mileage adjustment. However with that kind of mileage condition is more important really.
If it’s got FSH and has just had cambelt, water pump, pulleys etc (about 400-500 from memory) Then your 1800ish would seem about right in terms of value, possibly even a bit low.
However in my view t4’s are very overvalued for what they are. 200k plus vans are well into the region of going bang and needing a new engine/being scrap. Most vans with that kind of mileage/age would be into the hundreds. Check it’s had 10-12k oil changes and isn’t on the later 20k plus service interals. If you get it I’d do an intermediate oil change as well so every 5-6k as it’s likely to keep things running sweet for longer.
Oh and OT did you get any washers for your avid mounting?
