Man, definitely more expensive huh
Quite a bit.
In September 2023, before Microsoft nerfed conversion rates for existing GPU subscribers, I bought (20) 3 month Xbox Live Gold codes for $148.62. That converted to 33.3 months. So roughly $4.46/month. Granted that's when the 3 month Xbox Live Gold codes were on sale on cdkeys all the time.
Now the conversion rates for existing GPU subscribers suck, and are as such:
(Days of Xbox Gold > days of GPU)
30 > 15 = 0.5
90 > 38 = 0.42
180 > 60 = 0.33
360 > 114 = 0.32
720 > 152 = 0.21
* Numbers above are going to be slightly off, since Xbox Live Gold comes as either "months" or "years", and I just assumed one month equals 30 days.
So if you have an existing GPU subscription, and you want to extend it, the best option above is the 1 month Xbox Live Gold option.
That's why I said it's better to just wait, as the conversion rate for new members is ~0.66 (i.e. 3 years of Xbox Live Gold converts to 2 years of GPU). Caveat is you still need to buy a one month membership of GPU, on TOP of the Xbox Live Gold codes, so it will be <0.66.
Long story short, looks like the best you're probably going to do is about $75 for a 1 year Xbox Live Gold code. So $75*3=$225, let your existing GPU sub expire, redeem the Xbox Live Gold codes to your Xbox account, then factor in GPU 1 month sub (not sure how much that costs) to convert that to 2 years of GPU. Price will come out to roughly $10/month.
You'd have to buy (72) one month Xbox Live Gold codes to get 36 months of GPU (if you wanted to extend your existing membership), which would cost like $18/month (as I see one month Xbox Live Gold keys on cdkeys for $9).
You may just check and see how much actual GPU codes are on cdkeys/eneba/etc. and see if that's cheaper than the whole conversion route... Also obviously use MSRP for GPU as a reference point.
