Depends, what are you planning to mine?
(All the rates i'm posting are stock and not overclocked)
If you're going to mine ETH, the best bang for buck would be the AMD RX 580 - it gives you around 22 mh/s, your next best bet is the NVIDIA 1070 - gives around 27 mh/s.
I would recommend you go with around 4x RX 580's (don't forget you still need a MOBO, PSU, GPU risers, etc), so take that into account.
I would personally go for 4x or even 8x rx 580's.
I still not decided what to mine just confused.. I heard in a long term basis Nvidia cards are better because of many supported algorithms
And my budget is $2500
Soo I can buy x5 rx 580's or 3 gtx 1070 and rest $400 for other parts(GPU, Mobo, etc)
Btw thanks for the quick reply 😉