If u are not going to have any filter's u must HAVE little waste, so that means 1 or 2 fish max,
so if instead of a filter u do weekly water changes, u might get away with that if u dont overfeed ur fish, but I would spend the 50$ so that u can get more fish and some corals down the road(demending on ur lighting system)
and in closing u will spend the money on the salt and water to do all those water changes that u could of used to get a filter and do bi-weekly water changes I think the reasons why people do it with no filter is to say that I can do it
Goodluck and happy tanking