Some additional thoughts around costs for SWC:

Expenditures:
Initial salt costs: Assuming a 20,000 gallon pool needing 12 bags of salt: $55.00 ($4.57/40# bag at Lowes)

2-3 additional bags per year for dilution, splash out, etc: $15

Muriatic acid: $4.87 per gallon @ Lowes, using 6 gal/year: $30

Cost benefits:
No algecide addition
No buying/hauling/disposing of bleach bottles, splashing on clothes, eyes, skin, etc. (OK, you may need 4-6 gallons over the course of a year to cover high CL demands)
Freeze protection provided by my SWC control system (no closing chemicals, time spent closing, broken pipes, etc) Of course, this will depend on where you live
If you're a "gadget guy", then you get one more toy to play with and explain to your buddies during bbq's, swim parties, etc.

I don't think payback vs. bleach should factor into the equation to purchase a SWC system. Payback vs. being "Pool Stored" DOES factor in. But, if you're reading this, that's not a promblem for you becuase you've found this forum....