Lots of good advice hear; I'm also on the keep the car reliable & safe. I happen to be an advocate of low powered cars because you learn much more.
As an instructor I routinely tell students to stick the car in 3rd gear so we can concentrate on fundamentals, I will not be encouraging you to go "faster" I want students learning why the turn in points, apexes and exit point are where they are. Learning how to rotate the car using trail braking or throttle steering (stop making all the steering corrections and learn to put the car on a trajectory). Train your eyes so that you open up your field of vision so you're viewing the turn point, apex and exit all at once etc. It's possible to learn all of this in a Camry. Your choice of car at this point isn't that important beyond, as mentioned, it being reliable and decent to drive.
I've driven everything model Porsche from 356 to GT3, every version of Corvette from 72 to 2016, various 700 Hp Vipers as well as racing everything from Showrom Stock Miata to D-Sports Racer (now SCCA P2). I tell people all,the time a Miata is the most fun car you'll ever drive.We have $3500 in my son's 91 Miata it's stock except for Spec Miata suspension and the AC even works. Of course you need to fit.
I like the Golf but I'd want to make sure he still has the passenger seat as you'll need that. This car could also be morphed over to your wheel to wheel car.
Other suggestions would be an Acura Integra, Sentra SER, Mazda Protege or any other hot hatch. They're light and easy on tires.
Now as for your eventual race car choice; while I love open wheelers (currently I have a Novakar Formula 500) they're not accepted and most track days. I'd go with a sports racer if possible. Also do not rule any thing out. My wheel to wheel racing is done in vintage with my Datsun, one of my competitors bought an original Spec Racer (originals were Renault powered) these are widely accepted at both vintage and track days.
For the longest time I was the king of budget racing, our local SCCA events were double regionals, I would only do Saturday's race, ran on used race tires and only did 4 races a year. My season also included 6-8 auto-crosses and 3-4 track days. I did this for between $1500 to $2000. This was with our Datsun 1200.
These days I do 2 vintage weekends 4 track days with the Datsun and buy new Hoosiers once a year; I get this done for $3200-3500. After 30 years we've got $8500 in the car ( I save every reciept) I managed to make the top 5 overall and at track days I run the intermediate group (car makes 105 whp) and generally run faster than 3/4 of the group. I use the F500 for autocross and spend $1200 for the 6-8 events I do. I have $4000 into that car.
My total for the 12 to 14 events is $4400 to $4700. I have a 1990 e250 Coachman class B camper van tow vehicle (7k in the Van with $400 a year to run including insurance and registration) My open trailer is a single axle tilt that cost me $500 over a decade ago. The Datsun is 1600lbs and the F500 is 550lbs so the small trailer works.
So basically I have 20K (Van, trailer and 2 race cars) in vehicles and spend $450 a month racing. Note 3 years ago I was shopping for a 911 but instead but a Subaru Outback instead (we drive a lot of dirt roads) because that freed up money to buy and race the Formula 500.