What is the cheapest way to transfer funds between these two exchanges? Is it for example straightforward Poloniex (BTC) > Bittrex (BTC) or maybe something like Poloniex (BTC) > Poloniex (BURST) > Bittrex (BURST) > Bittrex (BTC) or else?
See, the transaction fee for BTC from one address to another is quite high. There is 0.18% exchange fee which is obviously 95% less than BTC transaction fee. I would suggest converting BTC to a currency with quick transfer times and low transaction fees like SIA, or UBIQ, or any other coin which will fit the profile and then convert it back to BTC (again with 0.18% fees) which will save around 85-90% in transaction fees of BTC.