Most people I know buy second hand TIs which aren't expensive. They are around the $20-50 (GBP conversion) mark here in the UK.
The Pi is not exactly a good proposition for a calculator either based on form factor and power usage. Also you really do need a tactile input system for calculators as they help avoid costly and confusing mistakes.
I'm not sure why there is so much hate for TI to be honest; they are very functional, very robust, have very good battery life and good resale value. I myself however use a $20 Casio 115/991ES PLUS.
I'm not sure there is really hate for TI calculators, but rather a general sense of "wtf are we paying for" when they've been the same spec and the same price for 20 years. No one really thinks they're bad calculators, but really they should be $20 by now, with a $100 color version or something to round out the high end.
The Pi is not exactly a good proposition for a calculator either based on form factor and power usage. Also you really do need a tactile input system for calculators as they help avoid costly and confusing mistakes.
I'm not sure why there is so much hate for TI to be honest; they are very functional, very robust, have very good battery life and good resale value. I myself however use a $20 Casio 115/991ES PLUS.