Another possibility is to buy games that serve multiple purposes.
A simple deck of cards is the most versatile piece of gaming equipment ever. There are hundreds of card games that you can play with a standard deck of 52 cards. Avoid specialty cards by playing Crazy Eights with your kids instead of Uno, then remove the queen of clubs to play a game of Old Maid.
You can also expand your indoor activity alternatives with a multipurpose game board that utilizes the same board and pieces for many different games. This certainly won’t replace classic favorites like Monopoly, but it’s a good way to supplement without buying dozens of board games that you’ll play once. A high quality board can even serve as decor.