@fab118 as austin3 said, you can update on the fly a database field. Use autobinding for this feature. In that case, bind the price input field to the respected database field of the product that has the price field. As soon as the user enters a price, the database will get updated. Of course this is causing calls to the database so performance wise this can be harmful when you have lots and lots of users entering prices at the same time.

Another option might be to use custom states in which you load the database values, enrich them with values in your custom state (using thins like :plus item or :minus item

If this does not help you any further, feel free to share your app and I will have a look