This is what yoshi means.
CODE
Players:
Force 1 (human force)
Conditions:
Current player brings at least 1 men to "get VIP pass"
Current player accumulates at least 100 minerals (cost)
Actions:
Set deaths for (unused unit) to 1
Subtract 100 minerals from current player(cost)
CODE
Players:
Force 1
Conditions:
Current player suffers at least 1 death of (unused unit)
Actions:
[actions you wish to use when they have access]
Preserve trigger
CODE
Players:
Force 1
Conditions:
Current player suffers at exactly 0 deaths of (unused unit)
Actions:
Display text "Guard: Your not allowed to go in there"
Preserve trigger
Yes you could use switches but you would need one for each player