Buck teeth or "Overjet" can be corrected with Invisalign easily. Of course it depends on how much space there is available between the teeth to begin with. In the old days we would pull a tooth to create space, now we do IPR..(sanding between the teeth) to obtain the necessary space. If you already have spacing issues then its fairly easy to pull them back into alignment in 10 12 months. Usually the fees are around $4500 to do this.
Consideration of the lower teeth is also important. If they are in the way of the upper teeth then they also must be brought back into the arch shape similar to the uppers...When it comes to treatment like this a consultation is always necessary to determine cost and treatment times. If someone quotes you over the internet then be very wary.
Hope this helps...Dr Thomas