Prestashop module for custom pricing

We need a Prestashop 1.6.0.5 MODULE built that allows for custom pricing to be entered on a product. Similar to this module - [login to view URL] The problem with this module is that when it's activated for a product if you don't put an amount in the custom price area it adds the product to the cart at $0, which is not what we want. On our website the product will already have base pricing and variations of this price incremented in a drop down list. What is needed is a 'free text' field to be added to every product that will only accept numbers, which if filled out will override the base price and add the custom price to the cart - eg: $126. If nothing is input in this custom field the product defaults back to the base price when added to the cart. I'm not sure but a radio button may be needed to turn this feature on/off on the front end, therefore making the buyer choose between the drop down menu with price variations or a custom entered price. This module will need to be able to be turned on or off for EACH product (so not a blanket 'on') on the Prestashop back end (CMS). Additionally the custom price field will need to have the ability to only accept figures between a specific price range - eg: between $20-$250 – which would be stated under or above the field on the front end product. If a number is entered outside this range the product would not be added to the cart and an error would be displayed stating something like 'Please include a price between $x - $xxx' (the set range). This price range will need to be set manually in the CMS for each product that has the module turned on. Feel free to ask any questions.