Word press web designer

I have a site at skillfulhire.co.uk but require a little tweaking to it. I recently added the "go saver" card option to my customers when using my directory site, but not all listings presently give discounts. I wanted to add a tick box (or some distinction the visitor can use) to select/search only those sponsored listings offering "go saver" discounts within a given category. Logically this would be on landing page and an obvious selection. How much would this be?