You can go look at the current S2 prices at the Nagrand/Netherstorm vendors (during S3 right now) to see what the S3 prices will be discounted to during S4 (including S3 offseason).
i.e. Shoulders cost 750, Helm/chest/pants/shields 900. One hand weapons 1300, offhand weapons 550.
It’s a good idea to go and plan now what you would like to buy in the offseason based on how much arena points you expect to have.
Original TBC T6 turned in for S2 pvp gear. There’s a post from one website that suggests S3 from T6 is highly likely. Esp with the shortened season, many people haven’t been able to finish a full pvp set, let alone multiple sets. When P2 of the Sunwell offensive unlocks on the PTR, the pvp vendors will be available, and we can check them then. Hyjal is locked on PTR so we can’t access that vendor to check.