IMO/E-Aquarium in general can be as expensive or as low cost that you want to make it. You can get creative and use non-aquarium items-provided that you are fairly sure that they are free of any harmful chemicals. Lots of different ways to reach the same goal IMO.
My soil based systems didn't cost all that much to setup or to maintain. I think my biggest cost was the lights-but even those didn't cost that much. I think I spent roughly $40.00 for the light strips and bulbs for my 75g and 55gal combined. I bought the shop light strips from wal mart and those cost $10.00 each and hold 2 tubes. I buy my light bulbs in the lighting dept-not the aquarium dept since all I need for plants are the correct color temp-that being..."Daylight" 6500k 40w since they are 48in tubes and 20w for the shorter tubes-The 48in cost under $8.00 for a 2 pack-a bit more for the shorter tubes...
So...$20.00 for 2 light strips and $16.00 for 4 light bulbs-total of $36.00. Then the added annual cost of $16.00 for 4 new light bulbs. Since florescent bulbs intensity is lost over time-this cause the color temp to change. The lights still work and we can see it and so can the algae-but the plants can't- to use it for energy and why you need to change the bulbs out every 12 months.
I collect my soil from my yard/pasture to use and that is free, I have used organic potting soil, top soil for the base and play sand, pool filter sand to use for the cap-but these usually are not too expensive and will go a long ways. The 50 pound bag of pool filter sand that cost under $6.00 has lasted a year or so that I used to cap several tanks. Same with the potting soil and top soil.....
I collect and use all kinds of things for my hard scape that I find around my property. Lots of different hardwoods and rocks to use for decorations and to tie moss and ferns to.
Plants for me was a one time investment-I spent about $40.00 and propagated from them. One good thing about live plants...they grow and reproduce....lol....
Then all those extra things-like heaters, thermometers and filters that can vary in cost, however, I don't use filters in all my tanks...that is the plants job on the most part-especially in my 10gal and under size tanks. Right now the only filters I have running are on the 2 big tanks-my 25gal and 20gal's don't have filters running anymore. I have them...just don't use them...lol.....
When you use nutrient rich soil-you usually don't need any ferts or injected CO2-The soil based systems are generally intended to be low tech, however, you can use higher lights, ferts and inject CO2 if that is something you wanted to invest in...Its just not needed on the most part IMO/E. I do have to add some extra Iron on occasion for my sword plants when they start to look tired-but even then it wasn't needed until the setup was near 5 years old and I made my own ferts by using the native red clay in my yard. I would dig up some clay-then roll up some clay balls-let them sit in the sun to dry-then cram them at the base of the sword plants-usually within the week the sword plant would perk and green up-usually sending out a runner or two to boot...lol....
Lots of different ways/methods to setup a tank....you are only limited by your imagination on the most part.....