How big is the home? I'm guessing around 1,100-1,300 SQFT? If bigger you may want to consider a bigger unit. The unit will probably be $1,500-$2,500. Double that figure for labor. This is assuming you don't have new duct work installed. Get a minimum of three to five estimates and don't let them take you for the duct work automatically. I would bet what you have is fine if the home was built in 92. At most you may need a little repair work and that shouldn't really cost anything. Hopefully I'm not off on the unit cost and cooling capability. I'm not real knowledgable on this I'm just going off what I was told when I went through the same process.