In reply to ogreville:
Difficult one. The newer once would make sense, but as you say, its at the top of your budget. The ex-Gas one also has its pluses though.....its cheaper, and I'm assuming its still got all the racking in the back....you could remove and sell this to help pay for having it painted into a nicer colour. They also have extra security locks etc. as well don't they ?.
Mileages aren't really a concern on either - they run like clockwork....I'm assuming they're TDi not SDi.
I'd go for the ex-Gas van personally. It'll have been properly maintained and will generally have had just the one driver. Vans and Ex-Rental aren't always the best combination. Sell the racking, paint it into a proper colour (this will get rid of wear and tear marks on the body as well) and throw the rest at a nice conversion.