It may not be unreasonable if the overhead to rent is high. It's coming down, though I have no idea what ranges are "too high" or where things currently stand relative to that.
If I have to rent a pickup to transport it back then I've got two choices. I can either rent the vehicle prior to looking at the item or after I decide to buy it for sure. If I always-rent then I'll kill at least 2hrs per CL purchase due to having to go to somewhere to rent said vehicle. If I rent-after-inspection I'll save those 2hrs when I don't buy at the expense of making two trips every time I do buy. Neither one is an attractive option.
Two hours according to what they pay me is no joke in terms of cash so in either case if this happens say twice a month I've paid for the total difference between owning a subcompact and a pickup truck: note, gas, insurance, etc.
I don't actually own a pickup truck and most of the time the things I pick up fit in my Forester just fine. But it's not unreasonable to make such a decision when you think through how much of a disaster it is to try and rent a vehicle on a semi-regular basis.
Absolutely. I'd definitely meant for that to be a part of "overhead" but it probably is worth calling out explicitly.
So it depends on how frequently you use a truck as an input into the cost of owning vs cost of renting equation. At once per year it absolutely makes sense to rent. At once per day it absolutely makes sense to own. Many use cases fall in between.
This is stereotypical penny wise pound foolish behavior. WRT to OP's relative hauling some plywood occasionally, for the price difference between a commuter car and a monster truck he could find a young man, pay his living expenses while he completes a complete carpentry apprenticeship, and pay the young man for some materials, and the young-ish journeyman could come out and do all the work for him as a thank you.
Another way to put it is the price differential is about 3x what I paid for a new roof on my house... all to haul some plywood...
When I put in a patio I had a flatbed truck deliver two pallets of bricks, two pallets of gravel and a pallet of sand bags. The delivery fee was roughly the delta between one months payment for a car vs a truck. You'd be surprised how much labor you can get out of a truck driver for $200 or $300 or so, and he was probably happy with me because the job only took him maybe 2-3 hours total.
The Ford F150 base model goes for $25k or so.
http://www.ford.com/trucks/f150/pricing/
A base model Yaris goes for $14k.
http://www.toyota.com/yaris/#!/Welcome
And that's presuming you're buying new! There are a great many used pickups for sale and the parts tend to change less frequently because pickup design parameters change much more slowly than car design parameters do. Because the design changes more slowly parts tend to be around longer and cheaper. And because the design of a pickup is driven by the need to have a 4x6-8ft long bed they tend to have roomy engine compartments in order to keep the proportions "correct"
By your own admission if you did at least one project per month requiring the use of a truck you would be spending the same amount of money. Perhaps that's money well spent to you, but you're not everyone.
There's no "right" answer here, only a spectrum of options that are better or worse depending on your personal preferences and the kinds of activities you undertake.