Need a mobile app to track fuel use and mileage across a company vehicle fleet

We run a small fleet of company vehicles and need a mobile application that lets drivers log fuel purchases and odometer readings after every trip, instead of the paper logbooks we currently rely on. Each driver should be able to open the app on their phone, pick their assigned vehicle from a list, enter the amount and cost of fuel at each stop, optionally attach a photo of the receipt, and record the current odometer value. The app needs to work reliably even with a spotty mobile connection, since some of our routes go through areas with weak signal, so offline entry with later sync is important.

On the back end, the transport department needs a dashboard that pulls all of this data together into a fleet-wide summary: total liters and spend by week or month, average consumption per 100 km for each vehicle, and a side-by-side comparison between cars so we can spot which ones are burning noticeably more fuel than the rest of the fleet. Ideally the summary can be filtered by vehicle, driver, or date range, and exported for our accountant.

We are open to either a native app or a cross-platform solution, as long as it runs comfortably on the mid-range Android phones our drivers already carry. Please share:
— experience building fleet or logistics tracking apps
— your approach to offline data entry and sync
— examples of dashboards or reports you have built
— a rough timeline and cost estimate