Application & Driver for device using a Serial Emulator over USB (Windows & OSX)

We are in need of a software developer to write a relatively simple application for communicating and configuring our new electronic device. The device connects using a USB cable, but has a USB Serial Emulator running on it, and all communication with it is via "Serial Communication". There is a working driver for Windows, which is just a .inf file linking the vendorID and productID to usbser.sys. (Device shows up as a COM port). We need a developer who can write us a user-space application and driver for both Windows and OSX. The application will do a few simple communication procedures with the device in order to configure it. We will provide the full communications API, as well as the source code to our current debug software which already does all of this communications. There must be installers so our customers can easily install the application. For Windows, it should work from Windows XP - Windows 8. For OSX it should work for 10.6 and up. We do need to have code signing and the driver will need to be digitally signed for Windows. We'd like the developer to assist us with that procedure as well (obviously, we will pay the code signing fees). We will provide a prototype device for development and testing. We need this project to be completed within 2-3 weeks. Our planned budget is $1000.