greetings
I'm very familiar with the subject of your project and I know that we can have a great partnership
let me set you an example:
the core of the devise can be an arduino uno ([login to view URL])
the speed data can be gathered by a GPS Shield([login to view URL]) and projected on a simple LCD 16x2 screen ([login to view URL]) that can be optimized (in terms of power consumption) . All the setup can be powered by a 9V battery (alkaline or rechargeable) that will be housed in a case ([login to view URL]) . The arduino c code is pretty simple and it is easy to be made bug-free. Logging can be implemented through usb-serial connectivity with your Pc ( I can provide you with a windows application that can have UI with data, controls, logs and save function).
Finally I can design a case for your devise that can house everything, even the battery (with or without the case that you can bye) that you can 3d print yourself or order it from a 3d printing site.
don't be fooled normally I wouldn't give all those features for the price you set so I would like your support in the Freelancer community which is something very valuable for me as a new member.
Please don't hesitate to check my portfolio.
My goal is to provide you with the most professional service possible.
I am looking forward to work with you.