Dell Power Companion WCKF2 6-Cell, 18000mAH - $53.80 FS w/Amazon Prime
Lowest price ever per CCC. Definitely the lowest I've ever seen it.
Not sure how long this will be good for, but does not require any extra steps or coupons.
Also at lowest price ever per CCC:
Dell 94TR3 Power Companion (12,000mAh) 4-Cell USB-C, $68.98 FS