Air conditioner dilemma

[Ed S.]

I am considering replacing a split system air conditioner/furnace in a 1000 sq. ft. 3/1 rental home with a new 2 ton AC unit and a 70k BTU gas furnace. The AC was not cooling when I bought the place. I plan to own this house for up to 20 years as a rental.

The prices I have been quoted are $3,500 and $4,000 total for time and material. Does that sound high? I have been told there are seasoned, licensed pros in Indiana that will do this job for about $2,500. If so, I haven't yet found them. What are your experiences? The units being quoted are not top-shelf. They are "contractor grade," and both carry a ten year warranty. One AC unit gets neutral reviews on line, and the other seems to get poor reviews. 

Both contractors said the existing system was holding a charge when they tested it, but they recommended replacing everything anyway if I planned to hold the property as a rental. The gas furnace was manufactured in 1955, and is inefficient by today's standards. 

This is a very simple house with a simple AC unit, and the indoor unit is about 15 feet from the outdoor unit. All venting is in tact and in great shape. 

I read a book recently where the investor rips out central air when he buys rentals because of the headaches they present. He allows window units to be used by tenants. I just replaced the windows in this house so I'm not sure I want the tenants jamming window units in. Does anybody delete central air from their properties like this? How much would it affect rent? What are your experiences with window units? Do they damage vinyl windows?