Who wouldn't want to drive a Ferrari if it only cost a few bucks more than the Toyota? I'm with Beagle get the best soil and ferts. Even at that your only out $50-$60. I grow ALL of my plants on either the bottom patio wall or the upstairs patio and my best producers by far are the ones in the earth box and them my home made earth box.
I initially set it up that way so I can go a couple of weeks between watering, but after a couple of seasons my 5 gallon potted plants produce about half that of those other 6 in the earth box setup. Total cost of my homemade box that's 30 gallons and holds 2 plants is around $25 without soil.