If you want the best deal with gamepass, get 3 years of Xbox Live Gold first. Wherever you want. If you have costco, I believe they sell a 2 year card for $90. Otherwise, I think newegg was selling one year codes for $50 each. Anyway, once you have 3 years of Xbox Live Gold redeemed on your account. Sign up for a one month gamepass ultimate. Should be $1. It will convert all your Xbox Live Gold time to Game Pass Ultimate. At the end of the day, you'll have 3 years of Gamepass Ultimate for about $150.
Just another tip. If you have the patience, sign up and take advantage of microsoft rewards (
https://account.microsoft.com/rewards/ ). It takes me like 2 minutes every day to complete pretty much everything on there and you'll accumulate rewards over time to redeem for various stuff.