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
The only easier way is to put instructions on your site (directly, or as a contextual pop-up) on how to add the bookmark as an icon on your home screen. This can be slightly more complicated on Android, and depends on the browser. A simpler option for your potential users is to provide a wrapper app via the Marketplace.
It is not overly complicated to create a simple wrapper Android app in Java that launches the browser, using Intents. The essential browser launch code is basically this:
Uri uriUrl = Uri.parse("http://www.yourwebpage.com");
Intent launchBrowser = new Intent(Intent.ACTION_VIEW, uriUrl);
startActivity(launchBrowser);
A more detailed tutorial for creating this is available here: http://mobile.tutsplus.com/tutorials/android/launch-android-browser/