populate field(s) after gform_validation

In my gform_validation I call a web service to validate form inputs. I'd like to populate form data (e.g. price) with a value returned from the web service. Is this possible?

I think I might not have phrased my question correctly. I have a form that needs to interact with a back end system. I'd like to be able to display information (e.g. price) returned from the back end system. The only place this seems to make sense is in gform_validation, b/c I don't want to call the back end service with 'invalid' data. My thought process was to allow Gravity Forms to validate the data, then I would call my web service which would do additional validation and if that passes return some data (e.g. price). I would then like to be able to display that information in the Gravity Form so the user can see it before they 'confirm' the purchase.