sponge filters are fantastic, and highly underrated I think, they provide great filtration along with regular water changes and help create a healthy environment for your axies. couple that with some hardy plants and your golden.
it will also aerate and filter the water without creating much current at all, a huge plus when keeping axies.
as for hides, they don't have to be fancy, try searching your yard for some rocks, and have a "play" and see if you can stack them into a cave, then cement them together with blobs of aquarium grade sealant. all it will cost you is a tube of sealant, (usually less than $10, well were I live anyway) and some time in the garden.