But if you're not going to that extreme, just get a few sponge filters and make a water bottle filter for mechanical. It'll be real cheap as well. Sponge filters are inexpensive (and can be homemade easily and very cheaply) and otherwise you'll need an air pump, a powerhead, some pillow batting and a water bottle
i think u should invest in a homemade internal K1 filter there are heaps of videos on youtube some use bottles some use tupperware containers depending on size required etc
the powerhead and sponge filter idea is probably best... an aquaclear 50 or 70 attached to an ATI hydro sponge 5 will filter anything up to about 50 gallons by itself ,adjust accordingly....and yes I use sponge /powerhead combos in several of my tanks