Switch is connected to the internet, you can buy games through the app store just like a phone. This is a lot more convenient than a physical game, plus stores are only going to carry the newest/most expensive.

Once you have a Nintendo account set up, go to the online store and there is a clearance section. You can get a ton of decent name brand games for under $10. I've got some for as low as $1. My daughter has now has more games than she will ever play for a grand total of about $50.

There is also a subscription you can get that gives online access to over 100 games from old school NES, SNES, etc.