I've bought one amber Grolsch with a Georgia top for $0.99 with free shipping. The seller was pissed that I won with the minimum bid and tried to charge shipping. eBay backed me up.
These prices are for bottle collectors, not homebrewers. I gleefully soaked off the remnants of the original label.
I've monitor eBay daily for swing-tops since 2009. Other than the amber bottle above, I've only found the larger lots affordable per bottle. I'm amazed how much even new bottles sell. It's cheaper to buy Grolsch bottles with Grolsch in them. Shipping is a bitch.
Drinking: Innis & Gunn Rum Aged; NB Conundrum Session IPA; Bush de NoŽl (Scaldis NoŽl); Innis & Gunn Bourbon Stout; Theobroma; Redhook Double Black Stout IV; Leftover ESB; Cuvťe Des Trolls; St. Landelin la Divine Inspiration; Hibiscus Mango Blonde.
Secondary: Victory HopDevil.