If you use GDAX (part of Coinbase) there are no fees. You just have to be a market maker and set your buy orders so they provide liquidity. I always hesitate to describe "the easiest" or "best" way to do something because it changes all the time. If it was me, I'd use GDax to get some BTC, transfer that to an exchange with high volume for STEEM (seems bianance is doing well based on CMC), get my STEEM and then transfer to my wallet and power up.