Good tractor overall. They get a bad rap sometimes based on the 1010 being a cousin to the 2010. The 2010 gas-engined version had it's troubles. The 1010 fell to guilt by assocciation. The 1020 spent a while climbing out from under that reputation.
1020's weren't overpowered by any stretch. I believe they're about 35 hp. At the time when they were new, the emphasis was more towards higher HP tractors. There were still plenty of 30 to 40 hp utilities on the used market from years past. So, long and short, there wasn't a huge market for 1020's. Not all that many built relative to larger models. But non the less, still a VERY good little tractor.
To answer your question as best I can, an average to slightly above average 1020 would probably sell in the $3500 to $4500 price range here in central Kentucky. Really good condition and/or with very good rubber, it wouldn't be unreasonable to see $5000.