Replacing a TRANE high efficiency XB1000???? Help

My ac recently went out on me and I am unsure about replacing it with a used unit for a lower cost, or going ahead and buying a brand new one. I'm selling my house in the next year and was hoping to avoid having to buy and install a brand new unit because when I had someone come do an estimate, they mentioned all of the added costs that would be needed to update my entire system throughout the house to fit newer models. My current ac was installed when the house was built in 1999. If I buy a used unit, what years or models would be compatible with the one I already have in place?? Please advise. :)
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