Check the 2 5g links in my sig - one's a Minibow w/ Whisper internal, conducive to the addition of a Colormax bulb or 13W screw-in PC and DIY CO2, the other is an AGA w/ sponge filter & desk lamp. I have a 25W Visitherm stealth in each.
A 5-6g Eclipse may be doable for $50, but w/ heater & other sundries, could go over. Also - the light is not that great (unless you get a screw in version of the hood as can be found in the older 6g hex hoods, and add a 10-20W PC).
Any way you go - small rasbora, shrimp, extra sm. Tetra species... just don't over do it.