Price seems O.K. But: Sonics have isues with the cooling system leaks and turbo failure. These are well documented in this forum and other sites.
I have a 2014 Sonic LT 1.8 (non-turbo) that I purchased with 60K miles and now has 102K. Over the 40K, the car had 4 separate coolant leaks and one oil bad oil leak. The last leak sent me over the edge and I gutted the entire cooling system and replaced every part that I hadn't already changed. Hopefully, I am good for a while. I have had other issues as well including leaking valve cover gasket, catalolic converter (replaced under extended mfg warranty), clear coat failure (estimated 4K repair), flex pipe, master power window switch, door lock switch.
In my opinion, I would seriously consider a Mazda 3 hatchback. a 2014 with similar miles is 10K. My wife has an 18, (same style) with 75K and has had no issues, It is a great car and fun to drive.
If you really like the RS, have a mechanic look at it and see if you can obtain service records.