Design a Simple iPad based POS System integrated with Weighing Scale to sell food by Weight

Hi We are opening a new high volume Indian, Thai and Chinese cuisine self service buffet restaurant in Central America and the food will be sold according to the weight. https://anypos.en.alibaba.com. Please check this website. They have exactly what I need. A screen, a weighing scale, a card reader and a printer and they are all connected. They just don't have the software and that is what I need. I want the system to work with a prepaid card and I want the customer to self check out through this system. Like a self service Kiosk. If it is easier, we can also use an iPad and integrate a simple weighing scale, card reader and a printer. Whichever way is easier, we will go with that. I will issue these prepaid cards myself. So I also need a hardware prepaid card system where I can insert the card and load credit or dollar value on it and sell it to a customer and then the customer can self checkout with this card. This system will be very similar to a small grocery store POS system. There will be only 1 type of food product and 1 price. It is a very simple and a single step and a single screen process as described below. After the customer gets his food, he will go to a checkout station, insert his card in the card slot (just like an ATM machine) and put the food on the weighing scale. The iPad screen will quickly show the credit balance and the dollar amount for the food on the scale. This info will be on top of the screen. In the middle part of the screen we will have 6 or 8 rectangular boxes for the drinks (We will need the option to remove or add more boxes) and all these boxes can start blinking 1 or 2 seconds after the screen appears, indicating to the customer that he needs to select a drink. The customer will then click the drink he wants and the drink and the cost of the drink will be added to the cost of the food. At the bottom of the screen there will be a button saying PAY NOW. As soon as the customer selects the drink, this Pay Now box can start blinking and as soon as the customer presses the Pay Now button, the total amount will be charged to his card and the card will be ejected from the system. The Pay Now button cannot become active until the customer selects a drink. The customer will "have" to buy a drink before he can press the Pay Now button and get back his card from the system. We will need to have an option for the customer to add more than 1 drink and or remove any drink from the list. This is the instruction for customers that I will stick at the station will be as follows. 1. Insert you card. 2. Place food on the scale. 3. Select your drink. 4. Press PAY NOW. 5. Take your Card and food. There are many "iPad based POS systems integrated with a weighing scale" but they have hundreds of functions that I do not need and many of them are very expensive. [login to view URL] I am attaching a diagram that roughly shows how our screen will look. Thanks Ravish Sony.