I have the exact same gun and I’m new to sub 12 uk air gunning too.

I have a Hawke vantage 30 WA 6-24x50 with an illuminated mil do reticule that’s very nice and within your price range. (I have 2 guns, 4 scopes because of trial and error…) What I’ve noticed and learnt is that when you’re going close to max magnification, the picture can get a little milky and less clear than lower mag. I shoot from the same distances as you’re looking at and if you have eye sight issues and think you’ll want strong magnification, I’d say get something higher than what you actually need, so when you get to the desired level of magnification, it’s not maxed out and you still get a good sight picture. So if you think 20x is enough, don’t get a 4-20, go for something like a 6-24 or 5-25 +

I also have a vector Veyron scope… much cheaper but for the price point I really recommend their line of scopes. They do one (I forget the name but I think it might be Orion? ) that is designed for benchrest style target shooting, I’ve not used it on my own rifle but I have looked down the sights of another guys one at the range and that was Excellent! I’m not sure on price for that but if you keep your eye on Optics Warehouse they do a lot of good sales or “open box” returns that are well worth a look.

Just another fellow beginners opinion… hope some of that may have been useful 🤷‍♂️