I would look at getting a used Trac Vac or Cyclone Rake to tow behind - you can use it for fall and spring leaf cleanup too. You can find these on Craigslist or Ebay from time to time for $700-1200.
The problem with the older decks is the speed and lift of the blades to push into the bagger setup. The newer cubs have higher air flow and faster blade speed on the newer cubs. You also dont state the size of your deck - 44-50-60"?
So you probably could adapt a newer Cub bagger ($400-600 maybe) but long term you are better with the tow behind vac system.