Purse bonus in Stalker Trials?

I’m a bit confused about this bonus, which seems to affect the score quite heavily. I’m inclined to believe it is connected to the number of attempts to clear a map. So I got these two questions.

  1. Is it indeed connected to the number of attempts?
  2. If it is so, can it be reset?

I’m asking this 'cause I seem to be stuck on the 4th map (7 robots). I can’t get the 3 star rating for the life of me and it seems everybody who’s got a top score also had a hefty “purse bonus”, which I cannot increase (stuck at 4600 or something like that).