A new feature being rolled out today allows the creation of subtrips and sublaunches. This allows you to sell multiple packages (possibly with different lengths, costs, openings, etc), that all are linked to the same trip. The benefits of this are you can run reports for the full trip or any of the subtrips, as well as only have one entry on the calendar. In the screenshot to the right (click it for a large view), you can see a sample where a deluxe package is being sold with higher pricing.
This update should appear in all accounts by tonight. You can hide the subtrip editor in the settings page if you do not plan to use it and want to avoid the clutter. Also note that this is a substantial update so there may be a few glitches that need tweaking over the course of the week.