I bought a preloved 7yo Toshiba from the local pawn shop for $AU50. It came with a 3 month warranty but is still alive 7 months later. Specs are adequate for my university studies.

Replacement 3 hour battery for $AU15 + shipping on ebay. I didn't check what a "genuine" one costs or if they're even still made but I suspect it would be more than I'd paid for the machine.