About how many units of botox (average) are needed for horizontal forehead wrinkles?

I am thinking about getting botox but was told that I had to pay $100 for a consult to find out how many units would be needed. I was told the cost is $14 a unit. I do not want to spend that much just to find out it is $700 plus and I cant afford it so I was wondering if anyone could tell me what an "average" number of units for HORIZONTAL wrinkles is. I am 37 and my wrinkles are not deep deep but they are visible at rest (when I am not making expressions). I do not care about the so called 11 between the eyes, just the 2 horizontal wrinkles across my forehead. If I knew the cost was $300 or less I would go for it, but I have no clue and don't want to waste a "consultation fee".