This app was mentioned in 2 comments, with an average of 2.50 upvotes
None currently since u switched to Android, but iOS had a few for free or very little. I had already graduated so I didn't really do much with it.
This one looks OK? https://play.google.com/store/apps/details?id=com.herbertlaw
The hardware costs (once you include the price of a screen, keyboard or keypad, and battery pack) might be as much or more than a new TI calculator.
If you can use a phone or tablet in class in place of a calculator Herbert Law's Graphing Calculator is an excellent Android graphing calculator.