You just missed this one. Plus the Red interior is more rare. Lots of 240's for sale all the time in the sites you mention and others.

https://www.ebay.com/itm/1972-Datsun-Z-Series-WELL-PRESERVED-RUSTFREE-RUNS-AND-DRIVES-WELL-/372582492765?_trksid=p2047675.m43663.l10137&nordt=true&rt=nc&orig_cvip=true

If you are looking for more of a project, and less of of a pristine restored car, you will be more likely to find something in your price range. Under $20 k is a project with rust and issues... Plus $30k is more of a rust free survivor or restored driver