With a little bit of legwork you can get an iPhone 12 mini on T-Mobile or Sprint for as little as $329 before taxes. This price hinges on other Slickdeals at multiple retailers so YMMV.
First time posting so I apologize if any of what I've said below was reported in another post.
At a high level here's the process:
1. Purchase an iPhone SE from Cricket Wireless for $49.99. Requires port-in and 1-month service for $60. https://slickdeals.net/f/14577712-cricket-apple-iphone-se-64-gb-49-99-with-port-in-new-customers-or-ex-after-180-days
2. Purchase 5x $100 Apple gift cards from Target. https://slickdeals.net/f/14559797-100-apple-gift-card-email-delivery-20-target-egc-100
3. Trade in iPhone SE at Apple Store and purchase and activate your iPhone 12 mini on T-Mobile to get a $150 trade in bonus. https://slickdeals.net/f/14444132-t-mobile-sprint-buy-an-iphone-12-mini-max-or-12-pro-with-apple-trade-in-and-receive-additional-150-cash-back-card
Below is the cost breakdown:
iPhone SE + 1-month service = $110
5 $100 Apple gift cards from Target = $480 with RedCard 5% savings, $500 without. Comes with $100 in Target gift cards
iPhone 12 mini = $699 - $210 trade in of iPhone SE. After purchase you'll get a $150 prepaid MasterCard.
iPhone SE - $110
$500 Apple gift cards - $480
iPhone 12 - $0 ($699-$210 trade-$489 Apple GC)
- $100 Target gift cards
- $150 T-Mobile prepaid MasterCard
- $11 remaining Apple gift card balance
Note that this price excludes sales tax charged on the purchase of both the iPhone SE and your iPhone 12 mini. It also assumes you have a number to port in to Cricket (can be purchased for around $7) and that you have a Target RedCard. You can also achieve additional savings of $15 if you activate two lines on Cricket (monthly service for 2 lines is $90). Lines can be cancelled immediately.