Maybe $1500 if compression checks out (leakdown test would be even better), and if it runs/idles through the warm-up period, the brakes are not seized, the forks are not leaking, all the electricals check out, and the chain still has some life on it.
The valve angles in this model tend to wear out the guides, leading to early smoking. (I had to rebuild the top end of one motor with 24K) I hear the valve keepers of the F2/F3 models are a poor design and when combined with the lean carburation, can lead to dropping a valve if you happen to miss a gearshift at redline. (search other posts on this topic)
The F2/F3 model carbs are a pain to rebuild and prone to clogging in hard-to reach places. I know - I cleaned one set 3 times before I took it to an experienced mechanic who finally got them running right. The accelerator pumps are prone to sticking, and like I said - they are jetted lean for low emissions, so these bikes are cold-blooded. (long idle on choke before they run right)
The alternator cover shown on the photo is not original, you can tell 'cause it's not black like the rest of the motor. That tells me this bike was dropped hard at least once, and repaired without much regard for originality.
It has a nice paint job. - that's worth something, the seat does not look ripped, that's good too. No matter how much you pay for a bike like this, unless you are a good mechanic, I'd still plan on spending at least another $1K to get it to a reliably safe running condition.
It's a nice start if you want to have something restored to almost original shape, but you'll spend another $2k and still only end up with a bike worth $2.5K in the end. If you buy it (at any price) do it 'cause you love the bikes, not 'cause its cheap. I got two of these almost free (a '78K and a '78 F, and have spent enough on them to buy a brand new modern bike. I could have been riding trouble-free for years, and probably have more beer money.
Have fun!
Six - Minneapolis.
