Curiously I weighed my two brollys only the other day . One is a Michigan 75 inch which I bought from Amazon when I first started out . It cost around £15. I have since waterproofed it but really only use it as a parasol in the summer( it’s perfect for that) and when rain but not wind is expected. For the money it’s very good and is now 5 years old. It does not have sides. It weighs 3k which isn’t that bad.
I also have a Preston Multi brolly which is 50” and much better quality for wild and windy weather so long as the wind is behind you. All brollys are useless if facing the wind. It weighs about the same with pegs.
The sizing is apparently the distance from the tip of one spoke up and over the top to the tip of the corresponding spoke on the other side. Thus a shallow brolly may be less than a deeper one. Nufish do one which only weighs 2k, retains heat and allows UV light through. Both of my brollys had spikes which were useless in hard ground and have been replaced by a solid aluminium spike by Gardner. A must imo.
Maver, Drennan, Fox, and others all sell similar. If weight isn’t an issue then stronger and heavier is best. Of my two the Michigan is best directly overhead and the Preston when pegged down. I hate fishing under a brolly and it’s use is a last resort. A poncho is a good idea to compliment a brolly . If a typical peg is tight then a 50 » maybe impractical so better to have a 45 » . I’d have 2 to suit different venues but then I fish different venues. NGT make brollys but I’ve never seen one but their gear is good quality for the price in my experience.
Have a look at KORUM brollies. They do a lighter one with side panels and fibre glass ribs. Any 50 inch brolly by the big names are OK.
If you dont think he needs side panels just make sure that an ordinary brolly has pegging points on the down side. Saves going boating when the wind gets up!
A problem you may find at the moment with furlough/lockdown a large number of people re discovering fishing and there are stock issues.
If you have a tackle shop nearby it may be worth ringing for advice. The large one in Hull is Angling Direct. They may be trading on a click and collect basis??
Beware of cheap and nasties on the ebay.
I use a Preston innovations 50" flatback with fibreglass arms. It's a good brolly ,but outside your budget. My other brolly is a 50" Daiwa mission, another good lightweight brolly, I pole pole fish as well as use rods, I only it as a flat back if raining hard behind me and float fishing,
As for zips in back panels, I have seen a few give up the ghost,