Hire a Website Designer

Good day I am building a website and still need some changes / modifications. My website is an advertisement for gastro-businesses, the site is still under construction and needs some adjustments. You have to customize the user area, it affects the general view and the design further information I will tell more precisely in detail. In addition, you have to change the payment option, currently, the payment options PayPal and bank transfer are available. But I would like to integrate another system which allows the user to transfer the conscience / credit by credit at the end of the month. With credit is mean the Pro successful processing As much credit the company is written to your account as it needs and this is multiplied at the end of a month by a factor X and the customer is indicated how much he has to pay. I would like to link my website to an app (Andorid & Apple) to offer special offers for consumers. I have to know how big the effort is to connect the databases and to program the app so you do not have the same view as on the website, but only special offers. At the moment, I have not got an app yet it still needs to be built up, first I need the information how big the work and effort + costs are. Please only contact me who REALLY know about this work and can also show me some examples of their work. !!!This price may differ important to me that I get the information I need.!!! Kind Regards Dusan