A:AnswerI use my cartridges much much longer than the printer warning indicates. Don't stop printing just because it says "running low". I've gone weeks printing well!
A:AnswerIt should be the same unless there is some online or in-store only special. Since they ship for free I always have them delivered since my nearest HP store is miles away. Just to be safe print a screenshot of cartridge you like with the price showing. Set your printer to print the date and URL too if you know how to do so. Take that with you to the store and they will typically price match if there is a difference.