Just a few things to consider (sorry for not answering your question):
- thick client requires maintenance on machines that are out of your control
- thick client is a pain to upgrade (you have to keep at least some backwards compatibility)
- server cost is a temporary problem that will go away, the decisions stay
- webapps are precisely the thing for non-technical users due to lack of installation and configuration on user side
- you need to transmit the sensitive information to the server either way regardless if they come from a native app or browser
- you are likely to keep the web interface as well having two products to maintain in the end
