How to Category Desc ordering by price(products with no price go to end)VM1.5.11

[immunity]

Hello in VM 1.5.11
when user press DESC ordering (by price) in a category
first appear products with "call for price" because they have price 0.000 (lowest)

how can i send these products in the end of the list and sort out Desc the products with price greater than 0.00 ?
should make 2 sql quieries first DESC with price values >0.00 and second with price value =0.00  but in which file? Or is there a magic button ?

[immunity]

in browse include folder (notable) it is printing the set of products (20 for example) using $product
in which file does the array $product get the values?