Here's a couple SPF's under $50,000 on eBay right now and they're local to me.
SPF w/392/Tremec, 18,568 miles and SB100 asking $49,995:
Other Makes Cobra Roadster | eBay
SPF w/392, 6,782 miles, asking $49,999:
Shelby Superformance mkiii Superformance | eBay