I think 128GB is the sweet spot for this phone. 64GB is too small given the size of today's apps and high-def video (and is not even an option on the iPhone 13 Mini), but 256GB (and 512GB for the iPhone 13) is too expensive for people who are looking for a decently priced phone.
RRP is currently $1,079.00 for the iPhone 12 Mini 128GB.
RRP is currently $1,199.00 for the iPhone 13 Mini 128GB.
Note: Amazon, JB HiFi and Officeworks are all pretty quick to adjust their online prices when one of the others adjusts theirs. It's worth checking them all before purchasing, but you will usually find them all at the same price.