It depends on your printer? Which is one reason I prefer Brother laser printers which are quite easy to refill. A bottle of toner costs about $5.-$6. You basically just refill, then reset the white cog. A few key presses on the front panel resets the page count.
BTW, I've found that manufacturers underestimate the life of toner cartridges. Most go on a conservative page count, which tends to leave un-used toner when they are supposedly out. Depending on the model, on the Brother printers, you can cover up the toner window with tape, or reset the cog. Also, reset the new toner cartridge settings on the front panel.
Personally, I'd rather just keep using the current toner until it runs out, rather than use manufacturer settings which tends to be way too conservative, and results in waste.