A good few hundred, I think. I remember seeing one advertised about five years ago.
Over the years, I've had various scans (MRI and CT and ultrasound). After the last two, the specialist pronounced that there was nothing wrong with the parts they were scanning, but they had found new medical conditions affecting two different parts of my body. So I have resolved to give up having scans......
But if you want a cheap private test, start with bloods.
There are so many issues that can be detected with blood tests these days and it is reasonably cheap to have it done privately.
PSA, HbA1c, cholesterol, thyroid, testosterone, heart disease, hepatic and renal function are the main ones that I have, although my GP or endo specialist does these.
You can pay a company called Medichecks do a comprehensive blood test for £250+ £35 (to go to a clinic to have the sample taken). It gets sent off then within a week you get the results, along with comments from a doctor.
Then you will be in a good position to assess your general health.