My Printer, an HP LaserJet P1006 is low on toner. Pages are coming up partially blank, or at least close to it, and the driver issued the warning. The replacement cartridge is CB435A.
Replace toner with a chip, is just under $20, a knock-off cartridge is slightly more. The few comments i have read say the knockoffs are never perfect.
HP has one at $67.99 or two at 121.99.
Amazon has the Dual Pack at $108.30 (it was $106.18 moments ago, reloading that tab also shows the new price), which has a $15 credit toward a next Amazon purchase. I use Amazon often enough to consider that a real $15. This means it's 2 at $93.30, or $46.65 each.
The Amazon price would be approximately twice the knock-off price, and i would have to buy two, which i don't go through too often.
Ebay has a few listed for about $53 with free shipping.
Buying the two pack on Amazon and selling the second on Ebay, sounds interesting. Assuming shipping is $4.90 though, (My cartridge weighs 18.25 ounces. Parcel Post prices for not-over-two-pounds to zones 1 and 2 is $4.90) making the total $51.55, leaving a dollar or two profit. Considering ebay's final value fees of 9%, however, makes it non-profitable even before ebay's listing fees and ebay's paypal fees.