I have a Lidl or Aldi copy of a Montane Featherlite. Little single-skinned flo yo thing that packs up into its own pocket. TBF I think it was only ever described as shower resistant but I have worn it in heavy, cold rain and it's a lot better than nothing, especially after I treated it with some wash-in Nikwax type stuff. It also is wonderfully breathable, as you would expect from something so flimsy! The zip is a bit dodgy now but I got 2 years' use out of it for only £8. One thing I've never liked about it is the elasticated cuffs, it's not so much that they're uncomfy but the rain rolls down the sleeves soaks your gloves, also they make it a bit more fiddly than need be to get on and off. NeilV's wife has one and seems to do ok with it.
But in the end I decided I needed something more waterproof and a bit more solid for winter, so I got the Rohan waterproof (Stormrider or something) on the recommendation of someone I know. The list price is about £195 which is probably ott but they have sales quite often. It's great! So far seems totally waterproof and more breathable than any other waterproof I've tried. I especially like the orange colour being bright but not garish, in contrast to say the Altura Night Vision garments. My only criticisms are that the zip puller can make a tapping noise against the jacket, especially when honking, which at first you can think is something about to break on the bike! and that the reflective strips on the back being red rather than white may be logical but is also pointless and reduces the nocturnal visibility.
But IMO even the Alidli cheapie montane-alike is more comfortable to wear than a standard 'outdoors' coat, which will tend to be waterproof but too heavy and the wrong shape, with pockets in places that dig into to your ribs.