Did I just read that correctly? Your building manager charges for the use of visitor spaces? I would want to have a look at that right away – I'm not even sure if that's allowed.
That aside, I wonder if a simple double gate “air-lock” solution might solve many of your problems, preferably with a boom before the gate so that the boom has to be down behind the entering vehicle before the gate opens. I know at least one building in Sydney that uses a system like that.
If space doesn't allow, I'm sure there are other technical solutions that would be a lot less than 100K.