I m not sure that the mentioned US$700-800 is valid in all parts of the country or for all model Trapdoors, esp. carbines, which are expensive. Most of the rifles that Ive seen in that price range in WA St & in CA are well used &/or abused. G & VG are in the almost 1k range & up.
Unless you really know what youre looking @, you can very easily buy a parts gun, w/ the wrong sight, wrong breech block, or a stock w/ an improper cartouch vis-à-vis the model & date of manufacture. Or worse, you could purchase that carbine @ the buy of a lifetime price & it is really is a cut down rifle
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The H&R Trapdoors have their own collectable niche & are increasing in value as they were a very well made firearm. Maybe increasing not as much as an original, but again, see #2, above.
Agree bout the RB, but they are also increasing in value.