It's because they are low/empty on stock, and it is essentially free advertising to leave them up at a higher price that no one will pay.
I emailed them this month about their spring listings, as the white ones and black ones were $85 but the red ones were like $380. They said they currently do not actually have any red ones in stock. (So I got white springs)
EDIT: Also don't hate on Advanced Auto much. They were literally the only place in the world that wouldn't rape me for strut-top nuts, for $1.99 each.