$1.50 a day I wish!!! I shop for iguana food at least twice a week, often three times as nothing ever seems to run out at the same time. And, I have to go to a store different from my regular grocery store as they don't carry the fresh greens that I want.
I would suggest that you look for other food sources if all you can find at walmart is collards. Yes, collards are a great choice for a staple green, but you need to add variety to your iguana's diet. Check around for other grocery stores that carry different choices such as turnip & mustard greens. Look for smaller local type stores where folks that eat "southern cooking" might shop. Odds on finding fresh greens are better where the locals shop. Health Food stores may also have a good selection if you have one in your town, altho prices are usually a bit higher.
Also, I can hardly believe that you can't find greens during the winter months. You aren't that far north that they wouldn't be available.
Check out this food chart for other HEALTHY options that you should be able to easily find.
You can add fruits & veggies to the diet without much trouble. Check the chart and see what both YOU and the iguana can eat and share so foods don't go to waste.