Ok, Brain Stirling you some how won and will make your boss look good. Short term, what econ advocated would have saved you an initial $200, but over the years, that initial extra cost will amount to not much.
In short, you could have done better, but thankfully you did not do much much worse.
But as the Admiral said to Jimmy Carter, why not the best?
That suggestion would have saved up to $200 but may not be possible in many businesses because of what you have to go through to buy it. In the long run, the cost per page on the 9120 is roughly 2 times higher for b&w prints. But in the original post, he did make it sound as if color was not an absolute requirement.
For the 9120 based on Amazon's current pricing, $48, for a 2200 page toner, it's approximately 2.9c per b&w page if the drum ($106) is changed every 15000 pages or 2.2c without drum changes. Compare that with the 1.4c and 0.9c that I mentioned earlier.
My math is like this:
(15/2.2 * 48 + 106) / 15000 = 2.888c
Given the short yield of the toners and your rate of consumption up to 5000 pages per month, you may want to pick up a few spares.
Another consideration is that of labor. If these toner carts have to be switched out 2 to 3 times a month, it will also be an expense because it requires you or other staff to take time to change it rather than doing their primary tasks.
I convinced my organization to spend $300 more initially for a more expensive printer because the toner lasted about twice as long. But also based on usage stats from the dying printer, the lower cost per page would make the printer less expensive (initial cost plus consumables) after 2.5 to 3 years not including the labor required to change out consumables. Also the printer had duplexer so there is there is less paper use making it more green -- generally good reasoning for my organization.
The restrictions Brian has are a bit unrealistic. For 5000 pages a month, I personally would not buy that one I suggested -- I was trying to stay within his price restrictions mostly. The MFC-9120 has a recommended monthly print volume up to 1500 pages which barely meets his 1000 to 5000 page per month requirement. Hopefully the printer does last a while because it doesn't seem stout for the environment where it is to be used.
If it breaks down sooner than expected, it could be a good thing because it can be used to argue with the the bean counters to get more money to buy a more robust printer.