From Quora: My Answer to "What is a good and affordable calculator for the SAT?"

Literally any scientific calculator would work for the SAT. You could even do the SAT with a simple calculator (like one you might take grocery shopping), or with none at all, but it’s not recommended.
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All you need is a calculator that works, and that does trigonometric functions. A graphing calculator, such as a TI-83 or TI-84, would also work, and would be helpful for graphing questions, and you can pre-load some formulas into those calculators, but you don’t really needthem. As an SAT tutor, I’ve been doing SAT math problems for years, and practically never use my TI-83, but a scientific calculator has come in handy (e.g., there’s no way to do inverse trig functions without a scientific calculator).
You can get a scientific calculator for not very much money - you can try any department store, office supply store, electronics store, eBay, or local site such as Craigslist, Nextdoor, FreeCycle, etc.

Here’s a link to the SAT’s official calculator policy, including a list of acceptable calculators (which includes “all scientific calculators”). SAT Calculator Policy