Consider using a fleece backing. It will cut your expense because you won't have to use batting, there will be a lot of sales on fleece at fabric stores as fall sales begin, and it's a lot less expensive than buying 100% cotton fabric for backing. At @ 58 inches wide you can size your blocks and border to be just under that width, and you can make as long as you want...a great lap size. Lots of people gravitate to the coziness of that backing.
For an October sale, warm fall colors might be appealing. Or something that looks cozy for winter. If you have a nice focal fabric in your stash, Warm Wishes is easy and looks more complicated. Or check out those great tutorials on Missouri Star Quilt Company and use your stash rather than buying precuts. Right now I'm using their tutorial for making a Summer in the Park -- rather than scrappy I'm using 3 different blues and solid white for the strips. It's pretty quick and coming together well...and looks like a harder pattern.