Just come back from 5 days there over new year. We were time limited and its a big place, so trying to get to the shops you want requires planning, and stumbling across stuff is unlikely.
Got some Levi’s in Macy’s, 2nd pair 50% off so a lot cheaper, but trying to find ones you like in right colour and size was a mare. Other stuff in there might have been cheaper but didnt find much we liked (american fashion is odd).
The GF got a Marc Jacobs bag from their store with a big discount, bloomingdales seemed more expensive for much of the brand stuff than the brands own shops elsewhere.
Vans, didnt find anywhere selling any significant range.
Rapha shop is moving to Soho (is/was at end of highline walk), just mentioning in case you wanted to go.
GoPro session, good luck. I wanted one and didnt see a single shop with one the entire time. In JFK they are $199 if you want to pick up on the way back.
Sales tax varies but seemed to be about 8% on average, its less on smaller things.