If you have Coinbase account, you are halfway through.
You could either follow this tutorial, which means you buy any of the available currencies in Coinbase or GDAX, then create a Binance account, send your purchased crypto there, and then exchange it to Steem.
Or you can buy either BTC, ETH or LTC in Coinbase, and then go to https://blocktrades.us/ to exchange your crypto into Steem.
If I'm right, @davemccoy has a tutorial on his blog somewhere. I'll go look for it.
Now I feel a little dumb. It's the pain meds making my brain fuzzy. I don't know why I didn't think of that LOL Thanks @simplymike <3
No problem. When I first started out, I had to do a lot of Googling before I was able to buy my first crypto :0)