Terry & Rene bring up valid points. Having had both diesel & gas vans recently, you'll spend less in gas w/ a diesel. I don't have hard numbers just yet (haven't gotten out the receipts & put everything togehter) but I can just "feel" if ya will, that I'm putting less money into the tank w/ a diesel.
With my gas engine, I was often putting over $1000/month. I'd have consecutive days where I might put in $85, $68, $82, $76 & so on. Sometimes I might even fill up twice in a day. This was to fill a 35 gallon tank.
Now, the price of fuel has come down somewhat, I'll grant ya that. Still, I've noticed (in a 26 gallon tank) that my fill-ups are in the $50 range & I'm filling up less often. I am staying local, but my miles aren't that much less in most cases & sometimes I'm even driving more.
My diesel isn't old enough to know how much the repairs will set me back yet (knock on wood) but I'd still think enough would be saved w/ a diesel to justify going that route. I do know that my former van had a $325 payment (payment & insurance) & the current one is about $1000 for those two things. While I'm less than thrilled w/ my van for other reasons, finances isn't one of em. The amount I'm putting into this van vs. my former one when ya factor in the fuel is about the same.
Providing the company I was signing on w/ would take any van, I'd get a 2002-2004 Ford Diesel if I had to do it over again. In my opinion that's the best balance between good fuel economy, new/used vehicle (ya won't have to replace it for a few years), payment, insurance, & reliability.
Good luck to you,
Danny