A friend of mine approached me with an idea for an app to plan and track your travel budget. First you would enter your itinerary, style of travel, and available funds, and get a rough estimate for the required budget. Then during the trip you can regularly update your available money, and get a dashboard with graphs and statistics on your spendings vs. the budget. The whole thing could also be integrated with other services to get recommendations for transportation, accommodation, etc.
If you have a few spare minutes we'd appreciate if you could fill out our survey, and there's also a little presentation to demonstrate how the app would work in practice.
I'd also love to hear about similar services/methods you're using for this at the moment, we haven't really found anything yet that provides this in a neat simple package.