Why not a low cost kit based on radiator temp?

Derale Cooling Products 16769 - Derale Performance Adjustable Fan Controllers - Overview - SummitRacing.com

Depending on which app, it looks like you place a probe in the fins. I'd think the controller would be able to replace the high-pressure sensor and trigger the slow speed fan via a switched ground. If the controller only puts out a switched hot, then you can re-use the same type relay from the 260.