WAG, a couple of grand, other things equal, including location and season.
But really hard to say, because “other things” never are. T4500’s are rare enough you just have to evaluate each one on a case-by-case basis. In the end that’s true of all vintage molded trailers. If you over-pay (within reason), but it’s exactly what you want and need and you have the money, it will all be water under the bridge a season later.
When we bought a 2008
Scamp 13 in 2012 with some minor, non-structural
fiberglass damage under the tongue and lightly oxidized gelcoat but otherwise like new, we thought we were overpaying at $4K.
Besides what we’ve saved on hotels over the years, which have more than covered the cost of the trailer and upkeep, the family memories are priceless. As one veteran member says often, “you can get more money, but you’ll never get more time.”