vintage calc for school work

[Dave Britten]

I'd also recommend finding out what sort of coursework you'll be doing and sizing your calculator needs appropriately. But vintage models are a totally viable option. There's not a lot you can do with that budget in HP land, but there are a few choices if you're patient with ebay:

20S - Algebraic programmable. Surprisingly capable.
48S/SX/G - These tend to be cheaper than the GX, which commands the highest prices of the family.
95LX - Has a bit of scientific capability, but the real draw is Lotus 1-2-3 and the financial calc. Not a bad choice if you're going to be doing finance or business math, or possibly stats.

If you want to look at other brands...

Casio fx-7000g - The world's first graphing calculator.
Casio fx-6000g - Smaller version of the 7000.
Casio fx-8500g - Like the 7000, but with more RAM and an expansion/printer interface.
TI-95 ProCalc - Really cool keystroke programmable with a lot of capability, though a bit bulky.
TI-86 - Probably my favorite of their non-symbolic graphers.