Prices seem to be all over the map for 50's motors depending on condition, and location. There are some motors I wouldn't pay $10.00 for listed at $400.00 and some I'd pay $300.00 for listed at $100.00. Anyway here's how I assess a motor:
-I first figure what I could get for the motor in running and cleaned up condition
-is it a keeper (how much do I like it) or a resale (if resale must leave a profit margin)
-will the seller let me pull the recoil and inspection plate to see the coils, if so then I can add or subtract based on condition and work needed. If he won't let me check then I assume they are bad and make the $100.00 deduction ($100.00 is the aprx cost of 2 coils and a tune up kit)
-is the motor generally desirable? Typically a 57 or 58 Fastwin will bring more money than a 59 or later model from a collector
-is the tank included and if so is it clean and rust free
-always deduct $50.00 for a new impeller unless the seller has a bill proving it's less than 5 years old
-if the seller will let you drain a bit of LU fluid a tiny bit of water is OK as that is condensation but if you get a tablespoon or so assume it needs seals and deduct $50.00 for the parts
Note: I assume that you will do all the work yourself, if you're going to take it to a shop best not to buy it.
As for this specific motor, in good shape I would start at a running motor price of between $250.00 and $350.00 then adjust down for everything you find wrong. The 59 isn't a very hot commodity on the old motor market, it lacks the style of the earlier models, but for a daily runner that you can depend on it's a hard motor to beat.
My 59 Fastwin Story:
I picked up a very sad looking 59 Fastwin for free (and trust me if it wasn't it would have stayed there) last winter. This poor thing was stored in the wood shop and had sawdust everywhere. I was just going to clean it up and sell it off but it was in such bad shape I figured no one would buy it! I did need a daily runner for my 14' fishing boat so I figured I'd check this one out and it needed everything, but the compression was good soooo I did the ignition, replaced the wires and plugs, replaced the broken recoil, replaced the carb with a good one which I overhauled, checked the impeller (it was new) drained the LU (nice and clear), spent an hour cleaning it up then tossed it in the test tank and it runs like new!
Here's before and after pics:
Note the tremclad blue tower and 2 hose clamps on the swivel!