Steph,
Good question about where to find the best storage containers. You've come to the right place. I'm (borderline) obsessed with them. One of my biggest dreams is to be completely cardboard box free in our house. We are getting close!
For plastic storage totes, my favorite places is, surprisingly, Lowes! I try to find those standard size (I think 18 gallon) plastic totes that I use for most of my storage for around $5, like this one here. I've had the best luck there.
Target and Walmat don't have nearly as big of a selection as Lowe's. They have a whole huge aisle (or 2!) dedicated to all kind of storage bins,...