It's an Airslot and doesn't look like a 20. I believe they were only produced in 16, 18, 21, and 24 footers. That one looks like a 18 footer, the 21 and 24 weren't produced as walk thru windshield boats as far as I know. I've never rode in the 18 footer, but the 24's had an awesome ride. $2000 sounds really high for a 35 year old boat that doesn't run.
I got got my '78, running for $1500. So yes it is a little high.
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'78 Cuddy with '82/'88 Johnny/Rude 150