My pool, like most of the pools I've seen, use an Intermatic
mechanical timer to turn the pool pump on and off. It does not seem
that there are any low cost digital timers available.

Is there any reason I could not use an irrigation timer and relay like
those used on sprinkler pumps? The only drawback I can see is that
its a bit more complicated to simply turn the pump on whenever you
wish using the digital timers vs throwing a mechanical switch.