Hi Jess,
Invisalign is a tool just as braces are in the application of correcting maloclusions. There are different tools that are best suited for correcting different maloclusions. The more severe the maloclusion and the time put into a case is going to determine the cost. The more severe the maloclusion, the more you want an orthodontist (person that has not only gone to dental school but has also attented a two to three year residency program in the recognized specialty of orthodontics) to correct it.
Bear in mind that Invisalign may not always be faster than conventional fixed brace. There are additional labs fees that the practitoner has to bear with Invisalign that are passed back to the patient so that the price is usualy higher than fixed braces. The main advantages with invisalign are that is removable (so that cleaning teeth is easier) and it is not easily visable. The down side is that it is harder to get precise movements in reguards to tip, torque and angulation.
Getting back to your question of overbite relative to cost, I would need more information. Do you need teeth removed? Do you need interproximal reduction? Do you need the use of elastic bands with your aligners? Is there any crowding and how much? Is there spacing? and where? Are there rotated teeth and how severely rotated are they. How many aligners has been estimated to align your teeth? As you can see, it is very difficult to diagnose your case and give an estimate. My recommendation would be to go to the Invisalign web site, find a well experienced orthodontist and get a second opinion. They are listed in order of experience.
Good luck!
