John:
The Bad
- missing original front rims replaced by small spare tires from car
- missing lights (one light post remains)
- no universal mounting frame
- no rockshaft assembly or lifting rod
- they say it starts but won't stay running
- missing start motor
Used rims and tires or just rims are pretty inexpensive and available. New tires from Tucker or Hamilton Bob's are a real bargain. Not much of a downer.
First the Universal Mounting Frame is part of the Cub-144 Cultivator and a few other implements and is not part of the basic Cub package. Not having it there is meaningless when it comes to the value of the Cub itself.
Head posts are pretty cheap, there is a pair of really spiffy ones on

at the moment and not expensive at all.
No Rockshaft assembly or lifting rod? These were also options that would have been associated with the Touch Control option.
Missing starter - starters were an option at one time. Magneto equipped Cubs often did not have starters since they used a hand crank and not a battery to start em up.
So that takes care of the Bad. Now to the Good
Having the Touch Control is a plus. As for the missing rockshaft assembly and the lifting rod, suggest you query him when you go see it. It may be in the barn or out behind the barn in the scrap pile. One never knows.
Having a good Cub-22 with the tractor is a plus.
Good tin, rear tires, rims and rear weights are all pluses.
This does not sound like a parts tractor to me but a runner. The problems associated with it staying running is probably fuel circuit related and a good cleaning, draining the old gas and making sure there is no crud in the tank or the circuit will solve it. You may find that this Cub is not a parts cub at all but a real runner.
Look for cracks and welds in all the usual places - that will determine the viability of the Cub. If no cracks or welds, then this one probably will be worth much more than a simple parts tractor.
Price - now it if was a non-runner with dings, dents, cracks, welds etc., then $300.00 to $600 would be a fair price in my mind. If this is a runner with all those good points then you have to add in their value as well - the Cub-22 depending on it's actual condition can be worth anywhere from $75.00 - $250.00. Without pics, it is hard to say, but if it is a runner then north of $1,000.00 will be closer and maybe $1,250.00 to $1,700.00. Again it all depends on condition. Location is a concern too - what is the going price for a good running Cub in Southern Ontario?
I know, it is now clearer than mud.