So, while browsing at Target this afternoon I stumbled across a bunch of mesh baskets and organizers. Picked this "Mesh Basket" up for $5.99!
It was pretty much just what I wanted. Something slim, halfway stylish, and cheap. Looks and feels pretty similar to the Topeak basket. Just zip-tied it on and now I can throw a bag of groceries or my backpack in there.
My only concern is that my thighs might hit the basket if fully extended. Maybe I'll see if I can push the rack back a bit.
(Men's 10.5 sneaker for scale

)