cheap adjustable pump

any recomendations as to a pump, whihc is CHEAP relitavly high flow, 500 gph or so, adjustable or dc, and preferably 3/8" connectors.

Based on my pump research before buying my pump, anything more than about 300-400 gph tends to be at least 1/2" or greater inlet/outlet. You could easily adapt larger inlet/outlets with threaded barb adapters though.

Good luck