Hello, I'm an experienced UK based Android developer, with a history in VBA / Excel / Access so this is perfect.
Ive had a look at the spreadsheet, and can pretty much figure out whats going on, and have a few ideas for UI, although It might make sense to wireframe first, should you wish to go ahead.
Although you have said lowest bid wins, I think that may be a decision you might regret should you wish to have a quality app, so I have bid at a good rate with the intention of providing an application of good quality / UI.
Anyways, let me know if you are interested, if not, good luck with your project !