Damn...$20 special ordered? Where?!
Just a chain-store LFS like PetCo/PetSmart, or a small LFS?
Low-maintenance/low tech. You won't need any special substrates...they would help, but if I'm thinking anubias, java ferns, crypts, java moss, etc...then they'll grow fine in almost anything.
Here's a long but incomplete list of things you could use as substrate. I've underlined ones I think would be suitable and cost-effective for you: Flourite, ADA AquaSoil, regular sand
, Eco-Complete, Soilmaster Select
...any of those would work. Aragonite would work if it doesn't affect water chemistry to a large degree.
If I were you, I'd go with a PC setup. For low-tech, I'd go with a 1x36W AHSupply retrofit kit. That bumps you close to moderate/high lighting, but I think you'll be OK. A full metal halide or VHO setup would be overkill. T5HOs will hang over the side of your tank (24" vs. 20"). If not a retrofit kit, I'd go with a 1x36W fixture from Coralife (I think they sell the 1x36w fixtures).
Do you think you'll ever upgrade to a high light/high tech tank? If so, we'll have to change your plan to accomodate for the change.