I have started looking but for me my current system is 30 years old and it was there when I got the house so I have no cost comparison to go by.
There are some knowledgeable AC guys on here. I am not one of them but a few things I can tell you from the search is you need to know the size of your unit or the size you need before you can price anything.
For me, buying my own 3.5 ton unit with 60k BTU gas heater is about 4 grand for a goodman unit if I install it.
Changing the heat from 40K to 60K was only a couple hundred bucks but to go from 2.5 ton to 3.5 ton was about $1000.
Do you know how many tons your unit is? Bigger isn't better, it needs to be the right size.
https://www.hvac.com/air-conditioners/ac-size-guidehttps://hvacdirect.com/sizing-air-conditioner-and-heater.htmlHouse square foot?
Climate range (i.e. Zip Code)
Gas Heat/Electric Heat?
Heat pump \ Split unit \ One piece unit?
Also there is a SEER value. The higher it is the more your unit will cost but the more efficient it is to operate.
Considering my local electric and gas cost is pretty minimal the seer value isn't too big a deal for me but if you are looking at a large unit in a high energy cost area it may benefit you a lot to get a higher seer value unit.