casio can do graphs on device for under $40

https://www.walmart.com/ip/Casio-FX-9750Glll-Graphing-Calcul...

The reason you can get used ti's for $30 is because that's how much they're actually worth.

You can get a catiga if you really want for like $17: https://www.aliexpress.us/item/3256809054964211.html

... or you can go with TI for $160 ...