Cst sales and purchase is same state

Both CST 2% is you will loss, ie on from purchase cost, oe from sale bill.

You can get the vat input by opening a branch at Andra pradesh

Movement of Goods matters for Interstate transaction, merely by raising Invoice will not account for Interstate transaction.   You can sell the product there itself but with local tax applicability.  This is casual trading once a while transaction, no CST-2% against Form-C applicability, its not going to be regular.  If its regular than register with the local sales tax authority.