Depending on the name brand and the SEER rating, prices differ from 1200 USD to 10,000 USD. The higher the SEER, the most energy efficient the unit will be. In the US the mimimum SEER rating is 13. Also to properly work the unit size, in tonage, has to be specific to your home size.
depending on what you want and the size of the house,roughly a total complete cetral heat and ac installation job for a three bedroom house with 1500 sq. feet duct work units copper electrical would be about $3500 to $5000
With the new energy efficiencies standards and you are looking at simple replacement you can expect 4-5000 dollars. If it is completely new system 10-12000 for a normal system.
You're going to need to open up the centerfold manifest which is located on the outside of the breaker. Reset the unit, if this doesn't work you've got an electrical cable problem, and the cable governing the breaker will need to be either replaced or repaired. Get a wire stripper and some pliers.
That would be dependent upon the size and brand of the unit which you purchase and if you are able to do a self install or have to hire someone to provide that services. Between $3000 to $5500