It is true that it boosts up the speed. However, each player has the same opportunity because it is an Event. Everyone can buy a card costing $5 in turn 1 or 2. You can save a coin when you only have 5 coins in Big-Money. You also can save coins when you only have 1 buy during constructing an Engine. I tried "cost $1", "cost $2+" (+1 coin token per a coin you overpayed), "cost $3", and "cost $3+", but none of those were proper.
$1: very very strong, broken
$2+: very strong, broken
$3: too weak (and sometimes it creates a large gap between 3-4 start to 4-3)
$3+: still strong, broken