While digging antique bottles may be the cheapest way to get them, it's a lot of hard work and you have to know where to dig.
Here is some help on digging antique bottles:

1. See Glenn Pochs' articles on digging/finding bottles.

2. The Bottle Battle is a digging story by Matt Schaeffer.

3. Historical Bottlediggers of Indiana operated by Jason Blevins, Email: jablevins@manchestertoolanddie.com

4. Just What are Outhouse Diggers?

5. Digger Dick's home page where you can click on his "Digging & Collecting Bottles Shortcut" with neat info on digging bottles.

6. The Secrets of Privie Digging is a book sold by Digger Odell Publications.
   Musings of a Privy Digger is an amusing/informative story published by Digger Odell.
   A Sprited Dig is a Halloween digging story published by Digger Odell.
   Can also contact "Digger", Email: jaok20@bottlebooks.com, with questions about digging and cleaning bottles.

7. Carl Pratt, Bottle Digger article from Antiques Near Me.

8. Spring Steel Probes (5/16" or 3/8" size) for $25 each. Replacement tips are $5 each.
   Raybrite Tumbling Powder for $5.25/lb.
   Contact Chip Cable, Email: chpcable@weld.com, Address: 235 Main Entrance Drive, Pittsburgh, PA 15228, Phone: 412-343-4955.

9. Spring Steel Probes 36-48", 1/4-3/8" diameter, "T" handle 1" diameter x 12" and ring 4" above tip, both welded. $35 including S/H. $3 extra for faster shipping. R.L. Wilcox, 7422 Park Drive, Mechanicsville, VA 23111, Phone (804) 746-9854, Email: wilcox7422@aol.com

10. MetalDetector.com sells treasure hunting supplies.