I'm not a Massey guy, I've never owned one. However, value for anything, and especially machinery, depends on so many factors, its hard to place an exact number.
I'd buy any tractor with a $100-200-300 price tag that shows potential, is complete and not stuck, and comes with at least one implement.
I'd consider any tractor that is in the above ranges that has all of the above plus good paint and originality.
Ask yourself this: does it run? If the answer is no, assume 50 bucks for a carburetor kit and maybe $20-25 for points and condenser, spark plug, and a good oil change. If the answer is yes, assume a score and move on.
If it runs, does it have full power and a good transmission?
How are the tires? Tubes are expensive, but $50 should set you up.
Does it come with an implement? Unless you plan to hunt down attachments special, finding unique attachments will be hard for some of the brands.
How is the "comfort" parts? Is the vinyl seat cracked and rotted?
That's only scratching the surface. Battery (or lack thereof) ease of starting, fuel system, charging system, wiring, gauges, lights, sheetmetal. Each factor says something about value.
Then there's the value to you. You might really like it, so it could be worth $500 to you when its worth $0 to me.
Let us know what you find!