Past experience:
Jan. of '13 I bought a 5500 Top Kick built in 2000, with a 12' flatbed and 336,000 miles. Payed $4,700.
I had bought a 20 cord load of logs the year (before buying a truck which is used just for deliveries), and processed into firewood but slow, slow sales without a means of delivery.
My intension was a good used 2500 or 3500 pickup, but prices were stiff and 10k and under looked pretty well used up. I read everything I could on AS and other sites about using a pickup and dump trailer for firewood. But in the end this truck for much less than a trailer/pickup combo, won over.
In part, because I wanted to buy other processing equipment that would either increase production or reduce my time and effort.
Looking back. The truck has worked out pretty well but realistically, cost about 2k (averaged out) a year to keep on the road (plates, insurance, annual inspection, repairs).
In addition to the initial cost, there were costly repairs over the five years, and expensive annual license plates at $500. Insurance, for commercial a truck is not any more than a pickup with basic coverage. The truck itself however is not covered. DOT registration is free. I think I paid $500. for a DOT ticket/education a couple years back. Another several hundred for compliance, name on truck, triangles, fire extinguisher, horn repair, etc. Annual DOT inspection is a few hundred, plus any repairs needed. Biggest expense was a transmission, as it was jumping out of two gears under load.
An important note. I got a DOT ticket leaving the state, as I passed the last exit on the interstate. I bought a nursery trailer and thought I'd do a three hour drive one way and save $300. shipping. My truck is now registered as intra-state with DOT. Meaning I can only drive on Michigan roads. To get interstate registration I believe you need to be bonded, unless the vehicle is your personal vehicle, and no other vehicle is registered to you, and you are not using it commercially. There are exceptions, like pulling a personal rv trailer.
If you get more than a 3500 educate yourself first, because their education is expensive.
And do not ask at the license bureau... The officer that stopped me said they do not know what they are talking about, they just hand out plates.
The draw back of an old truck is just that, it's old, and any money I've put into it is gone. It is still an old truck worth very little, even with a new rebuilt $5,000. transmission/clutch job. The 3126 Cat is fun to drive however...and I've had 2 1/3 cords on without overloading. It is very easy to get in places a dump trailer isn't going. Backing or turning around has never been an issue. But note I've only used it one winter and got stuck often after unloading. Just carried a couple buckets of ashes, some old tire chains off my dads '56 Buick that I lay on the ground, and a snow scoop. Never had to pull it out.