I've been spoiled by the Testors Mighty Mini kit, found at Walmart many years ago for $30. Still going strong for over five years I've painted 100's of N, HO, 1/25 scale buildings/locomotives/cars/rolling stock with ease and great results. My results seem to be at par or better than my other friends brands (single or double action) in the model railroading hobby, who use $100+ model master/paasche/badgers etc.
A good advantage is it's a single action brush, which are a lot easier to breakdown and clean, also switch nozzle sizes fast.
You can still find these floating on ebay for cheap, you'll also need extra bottles and different size nozzles.