There was a Mr Green in this area that used to design septic systems with out the expense of digging the drain field by using the space around the tank as the drain field. Certain soil conditions had to be met but he managed to get Pierce count approval. Anyone have more on this method?
Though you may save a little money by eliminating the drain pipes, the excavation would probably still need to be similar if you want the leach field to surround the tank. My concern would be the extra cost to repair it if it stops leaching. Having an easily accessible leach field would make more sense to me, and the cost wouldn't be significantly more.
It's rare enough that I see "ideal" conditions - where you can just leave the septic tank effluent dribble away on it's own. If the area is too broad then you won't get the spread of effluent for treatment purposes - if not broad enough you risk overloading the soil.
That said, I designed a constructed wetland about 15 years back - before the recent crack-down on regulations in this subject - where septic tank effluent was ponding beside the tank. We opened up a soil based constructed wetland; planted it; put in an outlet pipe and left it be. Total cost about €1000. No liner, since the ground was already heavy enough to lead to ponding. No percolation area, because the ground was light enough to permit some infiltration. It worked a treat. Not necessarily suitable for all sites, but this one was near the coast, so groundwater pollution wasn't a concern either.
This is something I'd love to see more of in future - low cost, low impact, low tech ways to get existing pollution problems solved.