Hello,
For those who have the same problem as I had, I could find a solution (not sure if the propper one, but it works for me).
So, go to your AdminImportController.php file and make sure that in the 247 line where it says:
'unit_price' => array('label' => $this->l('Unit price')),
and change it to:
'unit_price_ratio' => array('label' => $this->l('Unit price')),
Notice that 'unit_price_ratio' is the name of my Database column for this item (unit price). You need to make sure yours is the same. If not change the unit_price_ratio accordingly.
Thanks for the other suggestions that lead me to this solution.