My wife and I are looking to buy a duplex and live in one unit and rent the other. Some of these old city houses we've been looking at already have central air and others are getting by with window units. Obviously 80 year old homes didn't come with A/C and had to have it put in at some point. Could anyone ballpark a figure on all of the costs of putting central A/C into a place like this:

http://www.cbgundaker.com/search/advanced/detail.jsp?mls_num=354272&type=mf2


Don't need an exact figure. Just are we talking $10k? $20k? $30k? To do both units. Cost of the units, ductwork, labor, etc.

Thanks.