MS Store online for me did not like Firefox and had to use Edge to get to the details/add to cart page.
The only thing was, the online store said promo code was invalid - for anything, not just the mega bloks - so I had to call their phone support and eventually it went through with the discount. 1-877-696-7786
Also includes free shipping.
Mega Bloks Halo Covenant Drone Outbreak - $14.99
Mega Bloks Halo UNSC Attack Gausshog - $12.49
Mega Bloks Halo Scorpion's Sting - $27.49
Mega Bloks Halo Phaeton Gunship - $22.49
and there are a few others...