We have a website that offers an e-mail service. We would like to create a fully fledged app for this but cannot afford this right now. In the mean time it would be great if we
It seems to me like you need a mobile version of your web page. Do you have that already? Once you have your mobile website (ie. website optimized for mobile devices), you could create a simple application with only one WebView. All content would be fetched from your site and displayed inside a webview. This is trivial to make, however, making an entire mobile website will take some time.
Note that you do not HAVE TO have a mobile website, you could pack you existing website into a WebView, but this would lower user experience.