I would say that 7mm Rem Mag is the VERY upper pressure limit for a model 21 small-ring M98-type action.
In the end, "value" and "going price" are too very different things. The market place is very weird. The good news is that there are many SUPERIOR customized, semi-custom, and full-on custom rifles on the market that were PROPERLY built that often go for a song--keeping the smart and discerning buyers satisfied and happy. Then there is the factory mass-produced crap going for too much money that keep the not-so-discerning buyers satisfied and happy. Thankfully, my tastes have matured and I can always find a quality bargain. Enjoy that rifle. The Brno model 21 is considered the very best lightweight factory sporter ever made--largely due to that fine action and sweet shotgun style trigger guard. The stock is not as important (the originals were often quite bland), and a new barrel is an added plus (assuming it was properly indexed and headspaced and nicely blued).
If that rifle were mine, I would replace the bolt for a conventional Mauser 98 unit with a cut and turned down handle (saving the original of course), add a nice low-scope aftermarket right-side safety, a nice Timney trigger, and I would have model 21 iron sights and barrel band installed (if you can find them). Of course, that is a lot of money, and your rifle in its current form is still a fine piece! Definitely put a nice Leupold on her and toss that airgun scope.