put in air conditioner in ford focus
original 2003 didn't come with ac
I would suggest you sell the car and purchase one with A/C. IF you could do it, you would need to find the parts and do the modifications, which is mostly labor costs. Then you'd have more money invested into the car then you wished.
It would cost you thousands and be a major pain in the a**. If you REALLY want AC in this car, look up something like "vintage air" or AC for customs/hotrods. These are smaller self contained AC systems that can attach under a dash (still have to run a compressor and all that tho). It is not meant to be a replacement for the factory system, and wont work nearly as well, but it's something.