Hello,
Not sure that my answer will be enough to achieve your needs, but I think the simplest is this set of settings:
1. Define your product without price
2. Allow the free product to have a button.
in HikaShop Configuration => Main tab => Product part
3. Then process an override in your language file (If this is relevant to your product page display)
=> Learn
here
how to process a language override.
FREE_PRICE="
Free" for FREE_PRICE="
Quote request"
OR
For your add to cart button :
ADD_TO_CART="
Add to cart" for ADD_TO_CART="
Quote request"
Hope this can help you
Regards