There is a BIG debate in the other thread titled "Does anyone not like their SWG" that talks about costs/maintence/what is realistic to expect. An inground swg can cost anywhere between $1000-$1500 so i am not sure what the Aqua trol costs. Based on conservative estimates, including amortizing the cost of an swg over 5 years (lifespan average), electricity etc etc, you can expect to pay $21 (maybe slightly less in your case) a month to operate an SWG... that compared to $12-$15 per month it takes to bleach. Now this all depends on your own pool (size, how much sun it see's, bather load, the list goes on)
The bottom line is that it does cost slightly more per month to run an SWG, mainly due to initial costs and cell replacement after 3-5 years which can be $300-$400. Most people buy them for convenience... and a few other side benefits.