I just got this bag - so far it seems perfect.
http://www.amazon.com/gp/product/B005HR ... 00_s00_i01
$18 on Amazon.

IMG_9243 by J E, on Flickr

IMG_9245 by J E, on Flickr

IMG_9246 by J E, on Flickr

IMG_9247 by J E, on Flickr

IMG_9248 by J E, on Flickr

IMG_9249 by J E, on Flickr
It's slightly on the large side, but my picks are also slightly on the small side. Overall, I'd say it was definitely worth $18.
Open, It measures roughly 20x10". Closed, it's 4x10". It can accommodate a tool 10" long (the handle could be 1/2", maybe larger, around and still fit comfortably) and has 20 pockets, with an additional 4 'utility' pockets (2 on each end).