Using custom fields to modify product pricing

[robinmacharg]

When ordering a product I would like to modify the price shown in the cart based on a couple of custom fields. Two fields are necessary (interval - daily, monthly etc) and a number).

 

A user orders a product and provides the two custom field values. The cost is then calculated e.g. like this:

 

 

base_cost + (interval * number * unit_multiplier)

 

 

I *think* the correct place to do this is in the PreCalculateCartTotals hook but can't see how I would modify the product price dynamically since no value is expected to be returned from this hook.

 

Does anyone have any idea how I could go about this? Does this sound like something that requires an API-based custom order page, or does WHMCS support this natively?

 

Thanks for your replies.

 

Robin