That small RR is a tough bill. Someone months ago had a really cool little DIY RR 20 or 10.
If you are looking that small, I'd look into some of the all in ones. I like my Nano wave 9 pretty good and can find those cheaper than a biocube. Ideally upgrade the lighting at some point or go rimless sorta by just removing the hood and hanging a light.
Why so small? You could get a 29 gal for essentially the same price and not much more footprint, but its a lot more stable. Like fitz said, all in one nanos or biocubes are your best bet for that size range.
I REALLY dont like the all in one tanks so I am looking for a drilled tank it is not going to be a nice display tank so it dosent have to be pretty just hold water and be drilled for bulkheads (preferably on the bottom of the tank )