Hello,
Your current fleet management system needs to be converted a well planned web application.
I regret to inform you that this kind of application can't be built for a few hundred euros. IMHO thinking opposite may waste your valuable time and resources.
My proposal is building a responsive web application that perfectly fits for all screen sizes. After that it can easily be used in a web view for both Android and IOS and all types of devices.
I can also prepare the Android application that runs the web site in a web view.
The platform will be C# .Net and MsSql for backend. For mobile I offer Xamarin.
I will need your close support to understand the workflow in Excel.
If you agree we will be working on the project with pre-defined milestones.
I can present a recent project used by a company that has 70+ employees. We also implemented a mobile app that works fine, including a chat module and notifications.
Thanks for reading.
Halil