Do you think that swords will do ok in a pool filter sand substrate? I will probably end up using it cause it's so cheap and I have a lot of tank floor to cover.
They should. Echinodorus have very extensive root systems, and compaction of a substrate like sand is a very real issue with these plants. That's not to say it can't be done, just that it will take some additional care.
If cost is an issue, and I can appreciate that issue from my experience too, there is also bulk gravel at aquarium stores or landscape/stone quarry places. I got some very nice dark "birdseye" gravel for 75 cents a 2-gallon pail; to do my 90g tank is about 6 pails with some extra, that's $4.50 total. You can't buy enough sand for that, it is (here for comparison) $6-7 for a bag, it would take 2-3 bags for my 90g.
The substrate is important for many reasons (biological/bacteria, plant rooting, fish needs, and aesthetic), and once it is in and the tank set up, it is there for good unless you tear down the tank to replace it, so make sure it is right.