on the large HPIII, HP4, HP5, I found that the drum had to be replaced after about 50,000 to 200,000 pages printed. (If by the drum they meant the fusing assembly). It was a lot less on HPIIs because there was always current going to the fusing assmebly, it always was hot, the unit was never turned off, there was no electricity saving circuitry.
if you are printing 50,000 pages a year (or every 2 months), chances are you are a business, and as such it is a normal expense, and should be readily able to afford it.
I never use refilled laser toners. they do not work well. at least the HP refilled toners use real HP toner "ink", not the finer granulated "ink" in most refurbs. the refurbs tended to "leak", the drum/roller in it was seldom replaced, whereas the HPs were rebuilt, if necessary (and chances are that they would be).