Halloween doesn't have to be expensive. There are plenty of places to find stuff that can add a lot of unique detail to your Halloween yard haunt or party decorations. Many of them may seem obvious, but we're going to list them here just to have a centralized list.
Home repair centers like Home Depot, Orchard Supply Hardware, Ace Hardware, and Lowes (and many others) are great places to find tools and building materials relatively cheap. The best time to buy is during their sales. So, keep an eye out for their sales circulars and on-line sales.
Michaels, Beverly's, and other crafts stores are great places to find all kinds of stuff to add great details to your Halloween decorations and props. They've got everything from acrylic paints and brushes to wood accents and lettering to mini table lamps and faux vegetation. Normally, we think their prices are kinda high, so it's best to watch for their sales. These are great places to sign up for their e-mail newsletters which often contain 40% or more discount coupons.
Your local dollar store, Big Lots, or Goodwill Store are also great places to find just odd stuff. We like to buy stuff here that we fully intend to take apart, combine, or completely customize. These are great places to find some great inexpensive stuff, so they often scream out for experimentation. Some great examples are chests, clothes, vases & earthenware, fake plants & foliage, and even electronics.
Lastly, swap meets, garage/yard sales, and flea markets are more great places to find cheap stuff. Again, these are places to find stuff to experiment with, so don't be afraid.