The cost of treatment depends on several factors. Orthodontics for adults tends to be cost more than for children. The overall cost will be affected by the complexity of the case, the type of brace to be used, the experience and training of the orthodontist, the locality and the facilities of the practice etc.
To obtain a definite figure you will need to arrange a consultation with the orthodontist - this should not involve you in any commitment to proceed with treatment. The orthodontist will then be able to assess the problem, discuss the options with you and set out the costs.