It seems that Coinbase has recently enabled XRP, but unfortunately, only for Coinbase Pro users in New York:
Coinbase Pro announced on Twitter that Ripples XRP is now available on their platform. The announcement revealed that currently, it is available only for the New York user-base.
Source: https://www.cryptonewsz.com/coinbase-pro-new-york-now-supports-ripples-xrp/19386/So you would have to exchange XRP for BTC first (you can use Binance or any other popular exchange for that), and then transfer BTC to Coinbase for cashing in.
This is the best option you have to cash it
While depositing and withdrawing your xrp do not forget the Importance of the xrp tag
Be watchful you could lose your xrp if you dont include the right address tag