If you're looking for a cheap investment for a printer why not a full sized ink jet printer?
Something like:
Epson WorkForce 60 Inkjet Printer - Product Information - Epson Canada, Limited. Handling
It'll print 4x6 low quality at about 20sec per page. Ink you can buy aftermarket cartridges if you like to bring the cost down. Otherwise you'll need to invest in something more industrial.