First of all the system of treatment used is called clear aligners. Invisalign is an american company providing clear aligners. The treatment with clear aligners can cost you between 1lac-4lacs depending on the severity of the problem and company of clear aligners used. There are a number of companies like clear path, k-line, invisalign etc. Invisalign is the most expensive one.
You should know that unlike what is promoted by the aligner companies and general dentists, clear aligners can not be used successfully in all the cases. You need to consult a good Orthodontist to find out if you are a right candidate for clear aligner therapy.
The time duration for the treatment totally depends upon on how severe the problem is and what kind of tooth movements are required. So that can only be ascertained after a thorough consult with an orthodontist.