In most my planted tanks there’s a layer of plain old top soil capped with sand. Works just fine.
If you have a tractor supply store near you they sell black diamond blasting sand for a lot cheaper than pet store sand. Works perfect for aquariums too. If you do and go that way look for the 20/40 grit.
I think its around $8 or so for a 50 lb bag.
You could also use pool filter sand.
I used play sand, soft and natural. Didn’t take a lot of rinsing either. As for the dirt I dug it up behind my house in the woods.
I'm really happy I asked this question because it seems like y'all know a million ways to make the hobby cheaper
You’ll have to drain the whole tank and remove the fish either way.
Get your dirt and pick out all the twigs, bugs, stones etc. Mix enough water with the dirt to make a nice thick mud. Scoop it into the tank gently about an inch think. Get your sand, rinse it well and drain. Gently scoop and spread the sand at least an inch thick. When filling use a plate or bowl to pour water on/in. You don’t want to disturb the dirt or the water will be cloudy. Refill, plant and hopefully you’ll be good to go.
Word of warning, as left over organics and tiny critters die and rot in the dirt you can get an ammonia spike. Combat this with lots of live plants like duckweed, water sprite and wisteria. If levels start going up do a water change.
The problem with letting it settle is every time anything touches the bottom it just stirs it back up for the filter to remove at a later time.