I spotted Charmin Ultra Toilet Paper on clearance for $4.59 at my Walgreens store! Buy one pack and use a printable Charmin coupon for this deal:

Note: Clearance varies by store.

Use one $1.00/1 Charmin Ultra Soft or Strong Mega Roll 6 ct, Big Roll 9 ct, or Double Roll 12 ct or larger (coupons.com)

Final Price: $3.59, or $0.40 per roll, or $0.03 per square foot