Here is a Lotus Cortina on Ebay that is mint and has a but it now price of nearly $60k
http://bringatrailer.com/?p=672
Here is another for $60k
http://bringatrailer.com/?p=530
I would think a mediocre Lotus Cortina would be at least $30k
Were they regular Cortinas you were looking at?
Here is a regular Cortina, albeit with the wrong engine for $14.5k
http://bringatrailer.com/?p=661
It is perhaps a bit much to ask $15k for a car in the condition you describe though IMO