Hi there,

In case you didn't find any solution yet, you could find inspiration in following KB article:

Redirection option for E-commerce web site when adding product to shopping cart

The article contains also a link to the similar article on adding products to the shopping cart programmatically, which could be used for your aim too.

As for deleting the price from DB - that's not possible, since there's a fixed field SKUPrice in COM_SKU table. Easiest thing would be to set the prices to zero.
Then you could modify the transformation(s) that list(s) your products to not show the price at all (see some hints at Ecommerce Guide - displaying product price) - just by removing these parts of transformation code...

Later in checkout process, you could modify the controls so that the price field / column is not used. More details about this can be found at
http://devnet.kentico.com/docs/ecommerceguide/customizing_the_purchase_process.htm
and
http://devnet.kentico.com/docs/ecommerceguide/developing_custom_dialogs_for_checkout.htm

Hope this will help.

Regards,
Zdenek