I can't believe I'm saying this, but Walmart has great sheet sets. They don't last usually more than a couple of years for us, mainly because the top sheet ends up getting a hole scratched in by our dog who does the scratch and circle every night before laying down. I buy the 500TC, solid cotton or sateen sheets for our king, and they always have nice deep pockets and full elastic on the fitted sheet. Since we are in coastal Florida, and don't use blankets or a comforter, I usually wash our sheets every 3rd day. I know, we are weird!
I'd rather chew tinfoil than go to a Walmart store, but even I will deal with the extreme irritation to buy our sheets there, lol.