How much is this thing worth if it works? How hard is it to replace the blade? Are they a good thing to have or is it just a cool thing if you don't do much wood shaping or cutting? Its $150+tax and runs well. 1/2hp motor.
First things first, technically that's "just" a jointer. For some reason they were often referred to as jointer/planers even though they serve slightly different functions in a workshop.
The vintage table saw and (DeWalt) radial arm saw markets have taken a beating in the last 15 years and that has really trickled down to most powered vintage wood working equipment.
The one pictured is missing the guard and didn't come stock with the more desirable art deco style base.
With all that said, I'm guessing that $150 is at the upper end of fair. Maybe somebody else will know more.
Cutters for that tool are easy to get and cheap. There are probably several options for switching to a spiral cutter head. Is replacing an easy job? Not necessarily. You can spend a lot of time adjust blades, infeed and outfeed tables and the fence.
For that reason a lot of people take these vintage jointers and set the depth of cut and leave it once all the other adjustments are made. So it becomes a machine for milling a flat face and straight and perpendicular edge and not much else. Rabbets, bevels and longer jointing runs are done on other machines.