Check out shapeshift.io

I have used them for a couple transactions. You cannot go USD to Steem, however, you can trade bitcoin, litecoin, monero, etc for STEEM or almost anything else.

You don't need an account on their site. I'm not sure of the fees either.

As for Coinbase, that is the only place I have bought bitcoin and ethereum. It is a huge pain waiting but its very simple. Your bank card should work the same as a credit card though giving you almost instant access to you purchased funds.