I've had a HP1100 laserjet for many years (which I got dirt cheap when Software warehouse went bust), I think it was about 4 years before i had to change the toner cart, I'm on the second one and the printer is still going strong. Many places like Cartridge World will refill them, or have refilled/refurbished ones available too where all the moving and worn parts have been replaced, that might save a few quid on the costs, and where i got my replacement from (29 quid instead of 50 odd)
http://www.cartridgeworld.org/