The GDAX price is displayed on CoinMarketCap, but it’s not the official Coinbase website. They are two separate websites that are provided by different administrators.
Coinbase prices are generally higher than GDAX, but they can differ greatly depending on which exchange you’re using. Binance charges less than Bitfinex and doesn’t give away freebies like an extra $10 in bitcoin upon signing up for an account.
Is there a fee to sign up at Coinbase or use their services?
There is no transaction fee to go through with Coinbase right now, but if you want to do something else with your money (like transfer out of coinbase), then they will charge you real money for every single withdrawal! Some people might take this into consideration when choosing where to keep their funds but many others do not mind the idea of free transfers as long as they get paid fairly (cheapest).