I have a document portfolio with a cutout for a calculator, and I'd like to replace the existing calculator with a scientific calculator. However, it'll only fit calculators about 5 inch tall by 3 inch wide. Would be nice to know if there's a good scientific calculator that fits in that space. Doesn't matter if its solar, battery, landscape, vertical, or a bit smaller than the required size.

I bought my CASIO fx-260 SOLAR II about a year ago, and I think it's exactly what you're looking for.

(those markings I made are inches.)
It mostly stays in my pocket, but it is the first calculator on almost every scene of a math crisis I've been in ever since I got it.

Edit: They are $6-10 (US)
Note: This calculator is completely solar powered, so to use it, you're going to need quite a bit of light.