What's the best way currently to get the most time for the least amount of money on Gamepass?
Create new Xbox account. Sign up for $1 trial for your first month. Cancel recurring billing. Sign into Xbox or PC with that account, download and play games. When the trial month is up, rinse and repeat. Ideally, use a different credit card every time. You'll obviously lose your game progress between accounts.
Total cost: $1.00/month.
If you want to do it on the same account like a normal sane person, the best value is pre-paying for 3 years of Xbox Live Gold ($60/year, you might be able to find cheaper deals if you shop around) then upgrading your account to Game Pass Ultimate for $1 which will convert your three years of Gold to Game Pass Ultimate. Doing this method, you'll be out $181-ish dollars but you'll be good for the next three years.
Total cost: $5.02/month.
If you're already a subscriber and in the US, Best Buy and Amazon have occasionally run deals where you buy 3 months of subscription time ($45) and get 3 additional months free. So $45 for 6 months, or $7.50/month if you can wait for this deal to happen again. It's popped up about 4-5 times since Christmas.
Total cost: $7.50/month