IMHO throwing £300 at a present for a “very rich person” is a terrific waste of money unless you’re also moderately rich yourself. If I was spending that sort of money on a gift then it’d be for someone I knew well enough how to buy for without having to ask the Internet. (TBH, if I was spending that sort of money on a gift I’d be sharing a bed with them.)
So, think emotional / doing rather than $stuff. Do you have a skillset where you could make something, maybe? A couple of weeks of your time and some thought and consideration would be far more appreciated than throwing money at the problem, I’d have thought.
Failing that, activities; is there something you could do together even? Track day? Skydiving? Clay pigeon shooting?