If you really want commercial grade printing (more than 10,000 pages per month), then you should get a Ricoh or Kyocera.
If you can find a new Brother printer that accepts TN-580 compatible toner cartridge, then you should buy it immediately. That toner cartridge costs around $15 and prints upto 7,000 pages. The ink cost is less than 0.22 cents per page ! No wonder Brother discontinued those printer models.
The next best is Brother TN-660 compatible toner cartridge. It costs around $15 and prints upto 2,600 pages. The ink cost is less than 0.58 cents per page. OEM toner cartridges are the best but they are very expensive. Keep in mind that not all compatible toner cartridges are created equal. My personal recommendation are 1) Linkyo or V4INK, 2) E-Z ink, 3) EPS.
I own a Brother 5250 DN printer. It still works really well after 9 years. I also used to own Dell, HP, and Canon printers. The Dell printer has the worst reliability. Canon and HP printers are okay but their toner cartridges are little more expenisve.
