What you should consider before buying a laser printer
More importantly, for choosing the best printer for your needs, look at the supplies. If you are printing 5000 pages a m onth, and your printer has a 250 sheet paper tray, you are going to be putting new paper into the printer practically every work day. If your toner cartridge is rated for 2000 pages, you are going to replace that two to three times a month as well. Those toner cartridges are expensive. That personal sized laser printer is probably going to need its fusor changed a lot more often than the Lexmark T650n's standard 300000 pages too.
Look for a printer where you can get a high yield printer cartridge that will last you a couple months, minimum. And get a printer that has the ability to add on paper trays until you can pack a week's worth of paper into the printer at a time. For your 5000 pages of printing, try to get trays that add up to at least 1000 sheets and a toner cartridge that gives you 20000 average copies.
Find out what parts need to be replaced on the printer throughout its lifetime. There are drums, fusers, and rollers, filters, and sometimes developer, depending on the printer. Check fuser prices and the number of pages you can print before you need to replace the fuser unit. Remember, replacing the fuser can often cost half the price of buying the printer. However, the printer is a plastic box with trays, a few gears, memory, and the interface to the printer, without the fuser. When you replace the fuser, there is no reason why you will not get another 300000 pages of printing.