We looked at a vehicle for the church a few years ago, and the economics for an occasional-use vehicle just don't make sense. Among registration, insurance, and maintenance, a pickup or van costs at least $2,000 per year in fixed recurring costs. That's in addition to what you paid to buy it in the first place and margin costs (gasoline and extra oil changes, tires, and maintenance due to reaching mileage numbers before months). If we ever got in a bind and no mentors or parents or students had a vehicle to haul the trailer, we'd just go down to U-Haul and rent a pickup for about $20 per day. As I do the math, you'd have to rent the truck two days a week, every week, for rental to cost more than owning. Maybe if you do the CDW (collision damage waiver) it'd be an average of a day a week, but that's more than we take the team on the road.
Edit: We also purchased a trailer last year, thanks to a donation of over $9,000* from Ingersoll Rand Foundation. We've
wrapped it in some great graphics and added solar panels to power lights and charge batteries using "green energy". IIRC, it's the same size as Marshall describes below, and is at least 6'6" tall inside, which is great as Atlas (our 2015 robot), Perry (my son) and I all need within a couple inches of that to get around without crouching. (Oh, yes, a local company, Lewis Trailer Sales, also cut us at least $1000 off in the purchase and outfitting of the trailer!) We use the trailer for regionals as well as robot demos at city, middle school, and similar fairs. Sometimes, we haul it just to be a billboard. We may also take it out to be in a few Mardi Gras parades, though with carnival season falling almost completely within build season this year, that may not happen. (Carnival season is 6 Jan - Mardi Gras, aka Fat Tuesday, aka Shrove Tuesday, aka Pancake Day, which is 9 Feb in 2006.)
* Yes, I know.