Last year, as my truck was on its' last legs, I found a great resource at GSAauctions.com. This is a Federal government auction site where, among other things, trucks and vans are sold. Watching the site will help you learn what is available, and for how much.
There seem to be two main schools of thought...the "van" school, and the "utility body" school.
Vans are nice in that everything is out of the weather, and away from prying eyes.
Utility bodies are better for hauling large stuff, in fair weather make great rolling workshops, and offer better vision for lane changes and backing up.
Size is an issue. Too big, and parking is difficult. Too small, and you slow down on big hills.
Don't forget the obvious sources.....my "new" truck came from the power company. Just be wary....most used work trucks have been beat all to pieces. And be clear about what you need....for example, you probably won't need four-wheel drive, or dual rear wheels.
You'll probably be best served by something in the 3/4 ton category. You'll want it set up for towing. You'll want some sort of ladder rack and pipe carrier. You want REAL truck tires. And you'll want the truck low enough to fit into parking garages.
