There are archives of old sale ads here and at www.fiberglass-rv-4sale.com
. Yours is not a common model, so you may have to do some digging through the archives to find other Amerigos. Adjust for condition, season, and location. Realize that prices have risen faster than usual since COVID brought new people into the RV market.
It’s definitely not an exact science. Unfortunately there are are no accurate valuation sites for molded trailers. Most sales are private transactions, so there is little data for dealer-based services like NADA and KBB to track. They give values well below market.