"Calculators have come a long way since the first ones that could add, subtract, multiply, and divide. Now, for a modest cost, it’s possible to purchase a graphing calculator. Or, with your computer, you can put a free one in your browser."
Via Beth Dichter
Have you considered a different option? What about a block graphic calculator? This now a common way to teach coding, having students connect blocks together to build code. Blockly has a free online block calculator that provides math (a portion of the options are shown in the image), variables and logic. To the left side of the coding is the graphing calculator.
This type of calculator may help visual learners who may more easily create formulas through the use of blocks. Check it out at Blockly.
This is brilliant !