Yup! You can purchase Game Time.
Game Time can be purchased with real money or Blizzard Balance.
You can trade in your Retail Gold for a WoW Token - which can be used to fund your Blizzard Balance. At the time of writing this, the exchange rate is about 129 000 gold for 1 WoW Token. The amount you get on your Blizzard Balance when you spend the token depends on your region.
So if you have a couple million Gold hanging around (a fair few players did after Legion) then you’re looking rosey.
I did it - I’m set up for about a years worth of ‘free’ Classic. 