Build an Android + iOS app for my business

I want to make a simple mobile app with an interface to allow my salesmen to access a centralized costing center that will have an 'optimizer' to calculate lowest cost blends for NPK fertilizer sales based on costs that are updated by fertilizer plant and current logistic and product costs. The app will be completely stand-alone except for needing to pull the current variables set from somewhere. The app should be easy to use, with the salement imputting a few items: variable content of 3 main nutrients desired, distance from closest plant, and which of our plants it will be shipped from, and then the program will optimize the formula and give them a price basis FOB plant or delivered to the farmer's location. It will display the result direct and give two other options for micronutrients that can be added. I will explain in detail all of the variables and I need a back end to update weekly all of the variables. If the data is more than a week old I would like the program to do the calculation but return a message to validate pricing with the commercial director before closing the business. Please include pricing for the app, for both iOS and Android, including customizing and testing and also an hourly rate for updating and on-going maintenance.... I am attaching our logo and once we book I will send an excel spreadsheet that we currently use that has all the linear programming that will need to be duplicated...I can help with the math, but not with the programming. I am posting a value range but I have no idea what this will cost, please bid me what you think is a fair price and be advised that cost is NOT the only variable here. I want a solid, well-built app that looks good and is very user friendly for my guys. If you can do a mock-up before we book it would be appreciated, I am travelling this week but will check the bids and answer questions and try and interact as much as possible. I also need to know how long it takes as this is my first adventure into mobile apps. I looked for something similar and it doesn't exist. Good luck and thanks!