The brand name cartridge for your printer (HP) will generally provide better quality and compatibility. It is worth noting that some newer printers may block 3rd party toner and return an error upon installation. There is some information in the HP forums that indicates this may be the case for some printers.
Some things to consider when looking at the steep price for toner cartridges:
Laser toner typically yields well over 1000 pages, depending on the printer model and cartridge. This is why the cost can be much higher than traditional ink jet cartridges that just yield several hundreds of pages. Of course there are exceptions to this like the Epson EcoTank printer Kim talks about which can yield over 6,000 pages based on the model.
If you do not print on a daily basis, it is worth noting toner does not dry out or clog like ink. Because of this you are more likely to get the advertised yield rate even if you only use your printer every few months. In terms of cost per page, laser is generally half the cost of inkjet. So while the cost up front is high, it should last a long time and be more cost effective in the long run.
All that considered, as long as your printer does not specifically prohibit the use of 3rd party toner there are still good deals to be found. Just read the reviews and ensure you are getting a quality replacement as not all are created equal. We do not have any specific brands or sites to recommend for 3rd party cartridges, but hopefully this information will help with your decision!