Glad you spotted this dude. I did the same too.

For a little tip.... Coinbase owns the exchange gdax.com.
You can transfer money to and from coinbase and gdax instantly as coinbase and gdax are essentially the same pool of money!
You will already have an account at gdax if you are signed up at coinbase... they are the same entity.
You can set up limit trades on gdax will 0% fees.... yep, FREE!

Could have saved yourself the 1.5% fee.... or $30 in this case.
Now you know for next time dude.

Goodluck and all the best with your arbitrage! It works!