Simple shopify billing app

We need a private shopify based app, and what it should do is: 1) We upload our products to Shopify store, and once any of our product (based on SKU) get order, the amount is added to the app with a link of paypal to pay. 2) Same way suppose that shopify store get 10 order of our 10 products then, store owner should be able to select all order and pay for them together or pay for any of them. 3) In the app an option of 'express shipping' should be there, once tick, it ad $10 to the order. So once store owner select all orders and paid for it, we get email notificaiton with store name. Note: Price of ordered item to be added in app should be based on SKU numbers, for example if shopify store owner get 1 order of shoes, and one of socks from our catalogue then, in the app area he should see price like: Shoes: $42 socks: $10 Prices are simply derived from some kind of database, based on SKU numbers. My Budget is $500 as it's a private billing app for our products only.