FWIW,
I have 2 55 1st 4400's. Both run and are in good shape. (need paint and upulstry but are all there mechanically)
I paid $300 for the first one. It had been towed by the city and the owner was fed up. Needed new rubber and the fuel tank cleaned out.
$1000 for the second one with four new tires and two wheels in great shape thrown in. As near as I can tell, all original with the origional flat bed.
Mine didn't have as nice a paint job or interior as yours.
I am not a '57 man, but I'd say in my neck of the woods $2k would be a good sale right now. Not as many guys are into the big bolts and what guys are into them seem to be a bit short on cash right now. (At least I am!)
If it was me and I didn't have to sell her, I'd hang on for at least a couple of years until the market gets better. But then again, I'd never sell her in the first place

(My wife says it's a sickness)
Good luck!