I have an Outback, AND a LWD L400 Delica, and I think the Delica still deserves to be your front runner. Keep in mind I don't live in either one, but I've camped in them both enough to offer insight. And I've done this same analysis a bunch of times with the same and similar vans.
Prior to the Delica, I had a lifted 4x4 Ford Van (not quite as nice as that dreamy green one above) and mpg on a good day will be 12mpg. They suck to park, the highway ride sucks, they draw a ton of attention, and of course, the gas mileage is terrible. Outside of this forum, it's hard to find info on them for maintenance, mods, build outs, etc. But damn they are cool, there's no denying that!
But a L400? Parts are EASY to get. They just aren't QUICK to get. I order most of my stuff from Rising Sun Auto in Vancouver. Between them and Coombs (also in the same area) they have a ton of parts for these things. I just spent $480, including shipping from Canada for a new OEM radiator, OEM radiator hoses, and a block heater. That's not far off from what I spent to do the same work on my previous Subaru using non-OEM parts. Most everything is reasonable, but there are a few things (like the injection pump) that can get expensive.
I get ~22mpg fairly consistently, although it drops a tad when I have the roof rack and awning on. It can sleep 3 people and a dog without needing to do remove anything, and still has room for storage. The highway ride is great, it's easy to park and use around town, and while it gets some attention, it's not "LOOK AT ME" attention that the big vans get. For being 30 years old, there are luxuries that the newer vans don't have, like auto windows, heated wipers and mirrors, factory curtains, etc. But also since they are 30 years old, there's a TON of info online. US forums, Canada forums, UK forums, AUS forums. Videos, write ups, pics. Anything you need for maintenance or mods is out there and easy to find.
The market for these things is a bit weird though. LWBs are harder to find in the US. You can expect to pay between $10-30k, and there isn't a whole lot of sense in the price range. Getting a "dialed" one from Nomadic Vans in Idaho might be worth the higher range. Taking the chance on importing one yourself may be $10k, but expect to dump time and money to make it reliable/safe/home. The hard part is that rust kills these things before anything else, and that's really hard to inspect without someone you trust, or looking at it yourself. Hence where the higher end of the budget comes into play. But even then, you could have a really nice Delica for the price of a beat to crap used Transit. If you could even find a used AWD Transit in that range yet.