If you are lucky, that "rust" on key machined surfaces is greasy gunge, so inspect carefully! definitely some surface rust on the mounted chuck though. if the ways and lead screw are heavily rusted, then it's probably a parts machine at best.
IF the ways and backlash (X3) are decent, and IF is has ball/roller bearings and a LOT more tooling maybe $500 (since you are on TX and not the rust belt...)
But don't be afraid to offer less; it's a project, not a working machine.