It sounds like there may be two categories of teams here:
1) Need every possible available body, don't need to refuse anyone's participation
2) More students want to be on the team than the team can handle appropriately
For #1, recommend: No application, just an info sheet.
Keep track of time spent on the team; obviously this includes time at the shop, but should also include communitiy service hours, time at demos, time spent building the webpage, time spent contacting potential sponsors, etc.
On our team, we pay for the students' hotel room, some meals at Regionals if they have put in the required hours. If they fall a little short, they have to pay their own way. If they fall a lot short, they are not given an excuse to miss school to travel to/attend the Regional. You don't have to set the bar too high, but enough to "weed out" the student who just wants the occaisional Friday off school.
For #2, we really have little experience in this realm, so I ignorantly recommend: HELP START ANOTHER TEAM
