Apple refurb pricing is in line with what some other major resellers charge and Apple's phones are in better condition. With a new battery and outer shell, same 1 year warranty as new, etc. it's essentially a new phone for $100 less than current retail.
Apple Refurbished - includes 1 year Apple warranty, new battery and outer shell
Unlocked 128GB 12 mini - $579
Amazon Renewed Premium - includes 1 year Amazon warranty, guaranteed 90%+ battery life
Unlocked 128GB 12 mini - $629
Gazelle - excellent condition, includes optional 1 year Warranty Life device protection plan
Unlocked 128GB 12 mini - $554