I use sales at major retailers as stated above, and scouring FleaBay
Put an item on your watch list, and a motivated seller will send you an offer. Send a counteroffer and off you go.
I scored 4 pairs of NIB GP Turbo this way and paid less than $60 for each one.
Recently got the Wimbledon colorway of the Rafa Cage 4 for $85 from a major retailer. There is no reason to pay full retail pricing ever.