I actually agree that they shouldn't be charging £200 at this stage in the process. If BA paid that for each invited applicant themselves, it would only cost them around £500,000 (or the cost of around six successful candidates' training).
But it's a pretty minor issue in my opinion. As someone who has paid more than £13,000 over the past three years on flying lessons, it's hardly a significant fee for the opportunity it provides. In fact, my PPL headset cost me a good lot more than £200. And given that if you are successful the vast bulk of the training costs involved are covered - as well as being offered as close to a guaranteed job as you're ever going to get in this industry (for the best airline in the world to boot
) - it's a pretty amazing opportunity even with an initial price tag of £200.