And maybe the ductwork would need to be redone. You should do a Manual J and a Manual D calculation. IIRC, $49 for each for the online version.
may give you some idea of your expected yearly cooling cost at your location, and you already have your electric bills from which you can estimate your cost for your existing cooling system ($1 per night?).
In this case the new system may never pay for itself except in 'comfort'.