Three things, in this order. Where the outdoor condenser can go, because it needs air on both sides, a solid mounting and somewhere its noise is not pointed at a bedroom. Where the indoor unit can go, because it has to throw air down the length of the room rather than into a wall. And how the two get connected, because the refrigerant pipe, the power and the condensate drain all travel together and all have to go somewhere.
Air Conditioning is priced after the job has been seen, anywhere in the areas we cover. Send the postcode and a few lines about what it is doing when you contact us, and the answer comes back in writing.