Yep, active crossovers cost. Over here in the UK you can get something usable for about £130 pounds or less.

Of course, if it's possible with your kit, Uncle Daves technique should work fine.

A passive crossover circuit could cause a problem with a single bass bin as you'd be forced to mono unless you used a dual-coil woofer (that could be still be driven from a stereo crossover). I think Celestion do this with the 18" sub-woofer they have had out over the past couple of years.