I purchased my FFR mkII roadster about 4 months ago and paid 23,000 for it. I had been searching for about 10-12 months before I found the one I liked for the price I could afford. During my search I had only come across maybe 5 replica cobras for 18-23k. I found nothing under 18k.
I'll take that 18k back. You can find kits for 10-12k that ARE NOT complete. So if you found something for 10k you would most likely still need to finish it yourself (engine, tranny, paint, etc).
It seems there are a lot of roadsters to choose from in the 25k neighborhood.
When I first joined clubcobra there was a budget build that turned out super nice. I think his budget was 10k. I found the thread:
Owner built on a budget;
He did pretty much all the work himself including tons of fabrication and all the paint and bodywork himself. Way beyond my talents.
Good luck in your search.
EDIT: here are a few places to begin your search:
the classifieds on this site
ffcars.com
factory five forums
cobra country
carsonline.com
When I was searching for mine I checked all of those places everyday (except the ffr forums cause they didn't exist at the time).