Reddit mentions of Harmonia C-4500-NT Acoustic Cuatro Guitar, Natural

You can get a cuatro in the metro areas that have large PR populations(eg New York, NY, Bridgeport, CT). You can get a good playing one for around $300. It won't be this nice obviously. They are popular enough that big stores sometimes carry Mexican made ones like here or here. Interestingly enough the cuatros made with more modern construction methods and guitar tonewoods tend to sound more mellow and sometimes have more sustain and complexity. For solo playing it may be NOT to seek out a traditionally made one. These instruments are traditionally played in a band and must cut through all the other instruments(before amps existed!) so you almost want that hard brittle sound of the older style made ones made of the less sonorous wood(think Flamenco guitar vs a classical one). They are also meant to be flashy so the action is low to the point of buzzing a bit so that you can play them at lightning speed (again similar to Flamenco guitars). The instruments do not have bent sides like a guitar, but the back, sides and neck should be carved out of a single block of wood. The only problem with the old-style ones is the instruments do not fair well with seasonal changes. The neck on mine bent and shrunk to the point where the sides of the frets could be felt along the neck. Also the glaze crazed during the first winter(however I quite like this). The bent neck and frets required work to fix though. Sorry for rambling!