changing link for Call for Price products

At first glance it seems that the way to change the link that displays for "Call for Price" products is to edit the function "zen_get_buy_now_button" around line 1145. I see that that the constant FILENAME_CONTACT_US is coded into the function. So probably I can change the call for price button to link to another file by editing this.

However, before I do that, am I overlooking something somewhere in the admin configuration settings that allows you to control where the customer is taken when he/she clicks "call for price"?

In case anyone is trying to do a similar thing, here's what I'm trying to accomplish: some products are available only on a rental basis. I've changed the call for price text to say "Rental Item" but now I want the customer to open a pdf file (or maybe a new EZ page or some other html page) when he/she clicks on the link instead of the CONTACT US page.