The 999 Sportsman has long been H&R's top-of-the-line revolver, sorrily now also long discontinued (25+ years) - after the design was in production for over 85 years.
As long as one hasn't been abused, they will still be accurate & smooth shooters, that one should expect to have to pay $350-$450 for, in tip-top condition. ("Today", not once upon a time, way back when)
NIB specimans would undoubtedly bring more $$$.
In the last year, I sold two, one an earlier, solid-rib specimen, the other a later VR model, for $395 & $375, respectively.
IIRC, they were issued with either a 4" or 6" bbl, and some were made as single-actions only (Sportsman 199), and early Target Models & Specials were available in .22lR or .22WRF.