Lots of stuff here but for something useful.

Get a radio /cellular disruptor /signal jammer you plug in the cigg outlet. Wont be able to listen to radio or use your phone.

Old car if possible.

If not a basic Dacia is the least bad of the new ones.

Dare I ask what you are doing in your car that requires privacy?

Are you not wanting people to know where you go or are you beating off in the passing lane and don't want to make accidental eye contact with anyone?

Don't answer those questions actually. I will assume what the answers might be and respond to whatever my imagination gives me.

First things first, if you are beating off and don't want anyone to see, get tinted windows. One way mirrors would be sweet but are probably illegal in most places. They would be nice for those a-holes that drive at night and have stupidly bright headlights. I could really see myself in a car with mirrored windows that aren't one way mirrors.

Others already covered that phones track everything and your car is harvesting all the data it can. Driving without a phone is exponentially safer than with one. That's my opinion, I have no way to claim it as fact with any proof. Makes me wish phone booths were still a thing but I doubt one would fit in any modern car.

Even if you secured the car or found an old one that worked well, you'd need to avoid every camera out there and even things like billboards. Billboards frequently have wifi or bluetooth by the way. They track the cars that drive by and the people that walk by. Not just the noticeably electronic ones, take a close look at a billboard sometime, especially if you can see behind it. You'll likely find a device doing more than just powering spotlights on the crappy advertisement.

Unless someone invents a wearable Faraday cage that isn't obvious or constraining, you are not invisible to the all seeing eyes of technology.

If you want vehicular privacy so no one knows you are buying illegal drugs, you'll want to choose a place that's secluded with a good view in all directions to avoid ambush from cops or gangs. Alternatively you could do a place that's very busy, hide in plain sight. It depends on how much you trust your connection. I mean your drug dealer, not your internet plan.

If you want car privacy to pick up a prostitute in a place where prostitution is illegal, simply say you only wish to film a pornography. This makes you a director, not a criminal. Maybe. I'm not a cop or a lawyer.

If you want to be private in a car while you pick up a prostitute where it is legal, you can park beforehand and approach the individual or group on foot. You could also borrow a friends car or get a rental. It's legal, you really could do it with any vehicle. Don't hide your desires. Be free.

If you seek privacy in your vehicle to work as a prostitute, regardless of legality, you probably will have a difficult time obtaining customers. A custom license plate that is crafted cleverly enough might do the trick. You could also make an account on OnlyVans.

If you auto privacy is needed because your psycho ex is stalking you, go make some friends at the nearest gym and start carrying mace or a tazer. Wasp spray is a cheaper alternative to those. It has great range and is almost as effective at a fraction of the cost. Don't hide, it's time to fight back!

If your privacy needs when driving are because you are stalking your ex, don't do that, you psycho. It's time to move on. Let them go. There are plenty of fish in the sea. Don't worry if feel like you are going to die alone, because remember, in your car you are never truly alone. Technology is always watching. Even when you masturbate in your car.

Hope this helps, drive safe!

No privacy in new cars. So just forget about privacy and enjoy the car. They are so much fun and amazing to drive.

Advice is difficult, depends on price and preference. When I was buying a car, I spent every weekend test driving different cars. I think that's a good way.

Here's my advice: Don't buy a car. Ride a bike or take public transit. Walk whenever possible.