totally unrelated to the cost of purchasing the flatbed, but one more thing to remember to check into in your area is insurance policies if you have a flatbed. i'm not one to preach on the virtues of overdoing it on safety - on this forum i'm probably in the bottom 5%, based on all the concern and precautions some talk about taking - but here's one thing i found out a couple years ago.
first off, i don't make money with any of my equipment or vehicles - i have a vocation totally unrelated to them, so my policies are just basic homeowner motor vehicle policies. i was in the process of purchasing a ton truck with a dump to do a little work on a piece of property i had in a secluded part of the state. i was talking about it with a friend of mine, and a relative of his who is in the insurance business was there and told me to make sure i got a commercial policy for the truck. i told them i wasn't using it in commerce, and they told me it didn't matter. next day i checked with my insurance company and got the same story.
according to the two companies i talked to, any truck with a non-standard body requires a commercial policy. this means flatbeds, dumps, and whatever else you might have, with metal or wood bodies - even if it is for personal use only and not for hire. i didn't ask any detailed questions, but it makes me wonder about all the old 1/4 ton toyota and nissan pickups out there with engines that outlasted the sheet metal. add in all the old chevy and fords out there with rotted back bodies where people have made their own for them. my bet is that most of them never asked when they got insurance, and the insurance company never asked either. i've never heard of anyone having a problem, but you never know when the claim rep might be having a bad day.
i got the commercial policy for mine and the cost was really not much different than for a standard pickup, but the one other thing that is a bit of a hassle is towing trailers with the commercial policy. with my 3/4 ton pickup and standard policy, i have coverage no matter what trailer i haul - mine or someone else's. with the commercial policy i have to have each trailer i use insured for that truck. it's only a few dollars a year, but it means i can't just hook up to someone else's trailer and haul it. i do this often for friends - a few of them own their own trailers, but don't have a "good" tow vehicle, and for longer hauls, they ask me to tow it home if they buy a project vehicle. they usually want it on their trailer so they can move it around the yard after until they find a good resting place.
i'm just basing this on my experience. other companies or other states may have different regulations on insurance for non-standard bodies, but it is worth checking into.