Difficult to Price
In this crazy market you just don't know. Without seeing it I would opine that your 81 is south of $500, but who knows? A collector seeking to round out his 81 stable with that hard to find .30 Remington might bite hard. They are pretty common in .300 Savage and .35 Rem, neither of which is a big deal to find ammunition. .30 Remington is a different deal. The head size is unique to Remington so forming it from something else is out of the question, unless you wanted to down grade even rarer .32 Rem. The .30 Remington AR has the same head size, but is too short. Dedicated loonies are making the stuff out of .30-30 Win. by turning off the rims and cutting an extractor groove, one at a time, on a lathe. Long term, this may be the only source. Old Western Scrounger still sells loaded .30 Rem. I haven't bought any, so I have no idea where they get the brass to make it.
81's are beautiful guns. I treasure mine. They are quirky but reliable Browning designs made the old fashioned way out of forged and machined parts, the first successful sporting semi-auto (counting its predecessor the Model 8).