Hello,
I'm a UK based .NET developer, as you will see from my profile I have a number of years experience developing data driven web and desktop applications.
I can create for you an invoicing desktop application using vb.net with the database backend of your choice. You will note that I have quoted three days whilst others quote just one, this is because to ensure good feedback the application must be written in a robust manner - which I don't beleive can be done in just one day.
I look forward to chatting with you to understand your requirements completely, until then have a great day.
Regards
Damian