Tough call. I can't say I've seen a large group of collectors for that particular body style or year. I see trucks in the same years going for anywhere from 500-2000 in varied states of disrepair and with many more miles.

I'd say it would fetch anywhere from 2-5000 on the market. I probably wouldn't pay more than 3000, if I was interested in it. Not really my style of truck, so my numbers are probably lower than average.

If you are interested in that type of truck, you may look for 10 years and not find a better example. Super low miles, amazing color, pristine condition, and appears to be complete ready to go truck. Not sure of the market if you want to re-sell, but if you are going to keep it, that may be the find of the decade.

I was looking at Ford F150s and 250s before finally settling on the Bronco, years 74-79 primarily. Depending on condition they were listed from $3000-7000.
Beauty is in the eye of the beholder, but that looks nice. If it runs strong, it probably is at the upper end of that price zone.

Here are a couple similar examples from Auotrader Classic and craigslist:

It is amazing what a cool set of wheels can do . . .

I nearly bought a 1977 Ford Custom 4x4 Stepside, white, that was for sale in Brighton. Very little rust at all, about 60,000 miles, 400, 4 speed, wood box (needed restoration), ran strong, etc. $3500.
I just couldn't resist getting the Bronco though.

wow, that oil / gas money is spilling out everywhere

A Bumpside is the only generation F series I havent owned yet. I love them just as much as Dentsides and slicks. That one is amazing in its condition.