Most of these decorations I was able to find at my local Kroger grocery store. I also added extra home decor I had laying around the house.
Pumpkins make the best fall decor. These just so happen to be real, but you can find inexpensive plastic ones at the dollar store.
You can incorporate cotton into any season and it makes for a great centerpiece. Stuff any bowl or sugar mold with plastic pumpkins, fake or real leaves, acorns, corn...and it looks like you paid for an expensive centerpiece.
Leaves and pumpkins are all you need. SIMPLE. FESTIVE.