If this is really meant to be a one-off thing, then I’d suggest there’s no need to try and find any splendid nuances from an obscure micro manufacturer. Just go for one of the big names. My first suggestion would be the gold standard, Cohiba robusto. That might be a bit over your budget though. Second suggestion would be a Romeo y Julieta churchill. One of the most iconic cigars around and I believe it can be bought pretty close to £20. Third suggestion would be a Montecristo nr. 4. I believe it’s the most sold Cuban cigar in the world.
I think all of them are very good cigars and the only problem with them is that they are ”common” and a bit unimaginative. Everyone who reads about Cuban cigars for 15 minutes will stumble into those names. In your situation I would think it’s a bonus that the one cigar is very well known. If you’re not into watches but would like to buy one nice watch, might as well be the Rolex sub. Wouldn’t make sense to buy a Ressence as your only watch.
Disclaimer: it’s been about ten years since I actively smoked cigars and I haven’t had puff of anything in six years. My idea of pricing came from two minutes worth of googling so it may be really off.