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, boxes, crates, whatever your heart desires. I'm giddy just thinking of it!
One of my organization tips that I loooove is having different colored storage bins for different purposes. It's so awesome to be able to just look at the bins and know what they are for. Christmas decorations are in red totes with green lids, Fall decorations in orange totes, mementos in blue, seasonal clothes in gray. Soooooo much better than a sea of cardboard boxes!
I used to be kind of intimidated by home improvement stores until I started going with Brian. But, Lowes especially (Home Depot, not so much) has a huge selection of home decor items too like (tons!) of curtains, rugs, and mirrors. Check them out while you are there, if you need anything.
My favorite place for smaller organizing items is...Dollar Tree! There is one by me that has almost a whole aisle of plastic baskets, drawer organizers, and even fabric crates! It's AWESOME!! (sorry.. I get a little excited about organizing :) Definitely worth checking out. Also a good place for holiday decorations, cards, picture hangers, and umbrellas.
Important tip...assess your needs first and go shopping with a plan. It can be a little overwhelming and easy to just start buying up everything and then trying to find a use for it. You can easily spend a lot more than necessary.
Good luck! I'm proud of you for getting organized! Let me know if you actually find anything at those stores or if you find an even better place. I haven't actually bought any new storage containers in awhile. And I'd love to see before and after shots of your progress! And I'm on the hunt for large storage baskets for the baby's room bookshelf...no luck so far at Target, Walmart, Marshall's, or Michael's..maybe I'll check Lowe's next. Let me know if you see any while you are out!