I just bought my 98 for $16,000 with 64,000 miles. But it had all service records, one owner and super clean.
I would check www.autotrader.com and see how much they are going for there. I am sure they will have different price, but it might give you a ball park figure.
I got my '97 Black on Black leather Cobra with 46000 miles for $12,000. The tranny was a mess and the rear end needed new packing, though. The engine runs strong and it is in overall "very good" condition.
I just bought my 94 cobra, in mint, literally, mint condition(could be on the showroom floor), 37k, one owner (lady) from a local ford dealer for 10k. UK