Can you wire them up so that one is always on and one is manually controlled by a simple switch? So that I don't have to spend money on a davies craig thing and I don't have to try wiring it all myself...

yes you can... but you still need them hooked up to relays, otherwise the power load will burn the switch out..

but there are down falls with the fans on constantly or by a switch..
there will be extra load constantly on your alternator,
if you forget to turn them on the engine will cook..
if you leave them on constantly your engine temp might sit to low putting the ecu into cold start mode using heaps of fuel and lastly the fans will wear out quicker..

where as when you use a thermal switch the fans are normally only on for a few mins at a time..

Buy a thermofan switch from a 92 ford laser. it has a single pin that switches to ground at a preset temp. far easier, cheaper and more reliable than any of adjustable switches that you have to slip under a rad hose.

don't forget to have an A/C override with a diode relay.