Second-hand is the answer and the checks take thirty seconds.
Sit it on a flat surface and press each side. Any rocking means a warp, which is the only unfixable fault that matters. Run a fingernail around the rim looking for a hairline crack. Ring it with a knuckle: a clear note is good, a dull thud can mean a crack you cannot see.
Rust, even deep pitting, is cosmetic. Vinegar, a wire brush and a re-season and you have a smooth machined pan for the price of a coffee. I have never paid more than a few pounds for one.