Peat Moss and Gravel

You'd have to amend it with nutrients if you grow root-intensive (rosette) plants. Neither peat nor gravel have much nutritious value.

I do a layer of peat, enriched with Jobes plant sticks, and cover it up with some fired clay substrate. Fired clay like Flourite have a high CEC which helps to keep nutrients plant available. Gravel is a bit inferior in this respect.

Thanks wassers, I found the search function and it seems like peat also has a major impact on water clarity--that would be a deal killer for me. Do you have any experience with API First Layer Laterite? There's a shop nearby that sells it relatively cheap. I'd buy amazonia aquasoil but I'm kind of hoping for a less expensive option.

Keep reading, there's a lot to learn...

Peat underneath another layer of substrate doesn't affect the water clarity. Laterite on the other hand could lead to some issues when you pull out root bound plants.

Not sure how large your tank is, but keep in mind that investing in a "good" substrate can be a lifetime thing. I have used the same Flourite for years in different tanks and it is still good, if not better than when it was brand new.