It's unfortunately impossible to answer this question as it relies on a number of factors. If you are now in the military you're going to have an easy time through tricare - if you were previously in the military you should be able to get an MRI for free from the VA, but you may have an easier time utilizing medicaid or, if you're old enough to qualify, medicare. Additionally, if you're considering getting coverage through medicaid there are generally a wide number of requirements for eligibility that can range from trivial (I was automatically enrolled in green mountain care when I was an out of work student in VT) to extremely onerous work seeking requirements in some southern states. Medicare, if you're old enough to be eligible, is usually pretty guaranteed but you'll need to be near retirement age to access it.

The TL;DR is that you may be able to get it for free, but there's a very large proportion of the population that fails to qualify for medicaid and also won't have the financial stability to float $500 out of pocket and, if they happened to get one, wouldn't be able to afford any follow up treatment.

But I totally agree that the US system is an absolute breeze if you've got money to spare.