Scott,
I'll offer my thoughts, from a non-professional hobbyist woodworker that has a few motors he's bought, another 5HP 3 phase being worked on at the moment.
Single phase motors go for more $$$s, because, the majority of use can only use 3 phase. 3 phase is a double edge sword for most, but cost is never one since used 3 phase machines and motors go for less, typically.
As a rule of thumb, and this is only a rule, 3 phase motors are worth about $10/hp, but this doesn't hold true for small motors as yours. I saw as a rule of thumb, because there is no set price, and new 3 phase motors are no cheaper than single phase.
Typically people are looking for single phase motors to replace 3 phase motors in older machines, which can easily be done on belt driven machines. A direct drive motor needs to have the specific bracket/mount, but with belt drive you could always make a mount more easily.
I don't have much experience buying single phase motors, but know they go for more, and at some point if someone needs a motor, a new one could cost some $$$s. Those small motors you have sound good for a lot of things. I don't know I personally swap out a working motor for another, unless there was a big improvement. Look for machines that don't have motors, that's where you can get some good deals.
Have you used them? Do you have the switches/starters? I would definitely make sure they work if you haven't plugged them in some way and know they do in fact work.
Lastly, motors are often free. Sometimes good, sometimes bad...I have one I got for free, it's really old, I would like to see pics of yours. I don't have pics of this one, but I have a GE 1 1/2 HP Cast Iron motor, that must be made around 1920. I got it for free with an angle gear that came off some type of farm equipment. Do you need an angle gear? (just pay shipping!
)
This motor is bigger than a recent 5HP motor like a Leeson, Baldor, etc...it also has oil/grease tubs on the shafts/bearings. I'm gonna put it on a similar era
Crecent 8" Jointer.
The motor was given to me by a blacksmith who it was worthless to, as he doesn't have 3 phase.
For me it was a gem, since I had an old machine that didn't have a motor which it would be perfect for. One man's trash is another's treasure...
I did want a bigger motor, but in power...not size! This was a perfect motor for my machine though.
Seriously though, do you have pics of your motors? I can get a pic of mine to show you what it looks like, but not until too lazy tonight.