BMI is useless...
Different people in different places have different normal body sizes - some French girls around here would probably be classed anorexic in the UK, but it is their normal, healthy, size.
How much do you think Arnie weighed in his "Conan" days? Would he have been classed as overweight because BMI is too simplistic to distingiush between muscle and fat, never mind bone density etc.
.
Here's a much simpler test that costs nothing. We all go shopping. Find a mall with split levels (three floors is good). Now run up the stairs from bottom to top. If you can't make it, you're overweight - diet and excercise; if you're sweating profusely in an air-con mall, you're waaay overweight. If you make it but you're panting - excercise; if you're wheezing, you might want to think about kicking the habit... If you make it, you're fine. If you feel dizzy, or have to stop and sit down, you're underweight - eat more, and excercise too.
Now go spend that £120 on more productive things. Learn how to make a lemon drizzle cake, a proper hotpot, mitarashi dango, what all those E numbers mean and why many should be avoided, and how to make proper al dente pasta the *correct* way, accompanied by a sauce freshly made with tomatoes, basil, and rosemary from your garden...