I need a Shopify Developer for variable weight items

We are a specialty food store in NYC which is getting closer to launching our shopify e-commerce site. We have a few smaller things in terms of layout that we need done (this can be discussed secondarily) but our primary issue is that many of our items are sold as variable weight; i.e. 1 pound of ground beef. We capture the credit card at the time of order placement by the customer and then when we fill the order we would scan the package (preferably) or enter manually the correct weight as the 1 pound number is only an estimate that can be lower or up to 15 percent higher based on the credit card processor we are using. So lets say the item presents on the site as 1 pound for 9.99 per pound but the actual package we get from our meat department is 1.12 pounds. We need to be able to scan in the 1.12 or enter it manually as a replacement for the 1 pound number and have the system update the price (it already will have the per pound price) accordingly. This is what we are trying to do. It would be best if we could scan the 4 or 5 variable items and have the system realize which items those are (shopify's item number would be same as item number embedded in the label) and just update prices for all variable weight items at which point the order can be processed and the card charged properly and a receipt emailed to the customer. This is what we are trying to do.