REI offers the MSR Mudmat 2 Liner for $19.73. Opt for in-store pickup to dodge the $5.99 shipping charge. That's the lowest price we could find by $10. This portable tent floor has clips on the sides to attach to the tent stakes to keep it secure.
REI Garage offers the MSR Nook Gear Shed Vestibule in Green for $49.73. Choose in-store pickup to avoid the $5.99 shipping fee. (You can also pad your order over $50 to bag free shipping.) That's the lowest price we could find by $57. It adds 15 square feet of covered storage area to Nook tents (sold separately).