Can I get some air conditioning advice?

I have central air in my house and noisy neighbors. There are nights when opening the windows would be enough but the noise is too great. Rather than turning on the air conditioning in the whole house I was thinking about putting one of those air conditioners in the wall in the my bedroom. I would like advice about the in wall air conditioners. How expensive are they to run and how hard to have installed? Also, how noisy are they when running? As I am a light sleeper, I wouldn’t want one if it as noisy as those in hotels.

I do not want advice on handling the noisy neighbors – just on air conditioning pros and cons.