I'll toss a value out, given the little info and pics. Plus a few assumptions on my end.

As it sits, I'd probably spend less than 100 on it. Here's why, I can tell for sure that it's going to need tires, possibly tube repair, new handlebar tape, brake pads, cables, etc. and that's just to get it back to presentable riding shape. If I get there and the seatpost won't move, the stem won't move, the frame has damage (I don't suspect it, because though the pictures aren't great, the paint looks pretty good, but the rear wheel isn't installed fully which could mean there was an issue there, though likely just a storage thing.), or there are major issues with the components (broken derailleur, broken spokes, missing bolts), then I'd start subtracting off of 100 and possibly get to a point where I'm not interested.

I also like working on bikes like this and getting them back into shape and on the road for someone to enjoy, so factor that into the equation too, if you don't like doing this work, you'll should spend much less.

Once it's in good riding condition and the replacements/repairs are complete, I'd throw out 175-250 as a price range in my area, and that is assuming that the paint is in as good of shape as I think, if it is super scratched or rusty in spots, then subtract 50. People love to look good when they ride. 250 would mean great condition and that the frame is lighter steel as T-Mar said,

This bike is also pretty large, which could help because there's fewer out there, but there's also fewer riders. I like to sell things quicker, so keep in mind that is where my pricing comes from. I'd also likely drop the price after a week or two if there's little interest just to keep the bike moving. Now is the time of year when you shouldn't have an issue selling a bike unless you're asking too much.