My SO and I got back at 8am this morning from a whirlwind 20-hour trip to the SF Bay Area to pick up some furniture from my mom. The largest item was a wood-frame futon, which we were excited about getting because it means we'll be able to have a place for guests to sleep.
However, my SO and I own small, gas-efficient cars (highway mileage 35mpg for one and 40mpg for the other), and while we've managed to transport an incredible amount of stuff in our trusty small cars (including bookshelves, our entertainment center, and 6' tall garage organizers), a queen-sized futon would have been impossible to fit. Thus we rented a cargo van from Enterprise (with unlimited mileage), and in 20 hours made a sleepless round trip to the bay area to pick up the furniture. The futon fit inside the cargo van fully assembled (we pondered napping on it at a rest stop), and was protected during transport, all for $80 including tax and supplemental insurance.
On the road we were pondering that it was probably more cost-effective for us, and most other folks, to own small cars and rent a van occasionally than to own a pickup truck (and not have to rent a van), so when we got back we ran some numbers to test the idea. The difference in fuel efficiency between pickup trucks and small cars is large: the average small car gets 34mpg, while the average pickup truck gets 20mpg on the highway (data calculated from fueleconomy.gov's pickup truck and small car listings; large pickup trucks are apparently not included in the data). To make the calculations a bit more broadly applicable we found that the average employed person drives 35.5 miles a day in the US (data from US Bureau of Transportation Statistics household survey); we used this number for our mileage estimates.
Since the average US gas price is $1.92/gallon, small car owners save $1.38 in gas costs every day (0.72 gallons per day, assuming 35 miles driven); over a year this adds up to $505 saved (263 gallons of gas). Thus in only 58 days of average driving the average small car owner has paid for an unlimited mileage van rental for an entire day. This calculation doesn't include the increased purchase and insurance cost of most large vehicles, so small car owners likely save even more.
Since this is the first time in more than a year that my SO and I have rented a vehicle to haul something large, and we just got back from a 2,000+ mile trip to Canada, it's clear that we're saving quite a bit of money by having a fuel-efficient car, even though we have to rent large vehicles and pay for deliveries every now and then.