this is not as simple a question as it would appear. "Value" is incredibly subjective.
What you see listed on EBay is what the seller "wants". If you do an advance search and select the option to only show completed sales you will get a better idea of the reality of the market.
Please remember that they made quite literally millions of EACH model of these machines and they were built to LAST.
One of my favorite morning giggles is to do a search on my local Craigslist for "rare sewing machine" and then counting the 50-75 ads for "rare" machines.
I have seen 127's and 128's listed as "free to good home" and for $1000 on the same day.. (The $1000 ad has been up for more than 6 mos...)
Machines like this listed over $200-$250 tend to get shown on our "what are they smoking " thread.
With that said, the right machine on the right day to the right customer can be worth almost anything.