Low budget low tech - love it. I agree with the above, you might as well use the filter if youíve got it. But that doesnít mean you canít incorporate some Walstad elements. Dirt is cheap - on a budget just dig some up from an area you know isnít fertilized or mucked up with farm run off. Or just buy a cheap organic topsoil mix. Cap that with cheap sand (like pool filter).
As far as plants go, youíll hear about java fern and moss, as well as any anubias being low tech bulletproof from literally everyone. Duckweed is an indestructible plant that aids in water quality.
Dwarf sag will explode in dirt, almost to the point of annoyance. Green, brown, bronze, wendtii, undulata, etc crypts are also heavy root feeders that would love dirt and thrive in low tech tanks. Red dwarf lilies are a personal favorite of mine - easy plant to get red without extra iron, theyíll love dirt. You can pretty much abuse these plants as long as they have dirt or a root tab underneath.
People will also suggest wisteria, stems like hornwort/anacharis, or guppy grass. For whatever reason, these have always just melted on me until recently. Probably because Iíve started using liquid ferts on top of a good substrate. Maybe not. Idk, I donít care enough to test nutrient levels or get into the science of it all.
Stocking... youíll hear mixed opinions. Whatís ethical, whatís not, how happy the fish will be, etc. a lot of people only suggest a beta, nerite snails, or shrimp in a 5. Personally, I think that if youíve got ample filtration and heavy planting, thereís plenty of cooler options. 5 gallons of a nice planted tank would make many different kinds fish way happier than whatever boring, overcrowded tank they came from. But obviously there are better choices than others - not all smaller sized fish are ideal for nano tanks. A small school of ember tetras, any of the boraras, celestial pearl danios, or Pygmy cories would work. Sparkling gouramis, endlers, or a dwarf puffer are all other options. An emphasis on ample filtration and heavy planting though - plus weekly 30-50% water changes.