By all means head to Hobby Lobby and Michaels and check out their supplies...ALWAYS go to their websites and get their coupons for the week. One or the other generally has a 40% off coupon good for one regular price item...and depending upon the week there could be other discounts as well. I like to look not only in the cake section, but other hobby areas in the store as well...like the scrapbooking or the clay hobby areas for items like stamps and stencils and such that can be applied to fondant and gum paste or cake decor. I got my fondant tools in the clay area for a heck of a lot less than it would be in a 'cake' section. I also look in the bridal areas.
Don't limit yourself to just the cake areas and you'll find a lot of things that can be adapted to cake use! Michaels carries only Wilton gel colors...Hobby Lobby also carries Americolor gels in addition to Wiltons. Michaels has lots of ribbons (I use for around the cake boards and sometimes cake) and they are often on sale.
I always forget to go to JoAnn's so I don't know what all they have in the way of cake stuff. Walmart has a very limited supply of things...though I did notice they were carrying more molds (Wilton) the other day. They only cater to Wilton items.
We're lucky enough to have two sugar art supply stores that carry a variety of molds and other items we used to have to order off the internet to get. So be sure when you're in an area, look for 'sugar art supplies' and not just cake supplies when you're out and about.
Good luck, have fun when you're here and don't forget those coupons!