Unfortunately, the sub £50 market is a bit hit and miss.
four cases i can comment on.
corsair 200r - This has great cable management and has the motherboard stand off's already installed. The major downside with this case is that the cooling is not good at all when using the stock cooling configuration and the 2.5/3.5 inch bays are made of plastic with the ssd mounting casuing ssd's to run hot
Antec one - I have this case and it is great in many areas. It is very well built, has awesome cooling and has proper 2.5/3.5 inch bays. The 3.5/5.25 inch bays are tooless. The major downside with this case is that there are no fan filters and the cable management is basic. There is no dedicated hole for the cpu cable and the holes in the motherboard tray are not that big either being slightly covered by an ATX board. There is a fair amount of space behind the motherboard tray but not loads and, depending on where the cpu power socket is located on your motherboard, the cpu power cable could clash with the top fan like it did with mine.
NZXT source 210 - Like the antec one, this has excellent stock cooling with good cable routing but it is extremely basic in what you get. There are no fan filters, no rubber grommets where the psu is mounted and there is also no 2.5 inch drive bays meaning you will have to invest in an adapter if you want to mount it properly. The clearence for the cpu cooler is not great either at 160mm. I cant comment on the build quality though.
Zalman z9 plus - This comes with the most amount of fans and looks like a gaming case the most. its Very well featured with a fan controller , cable routing for all major cables and comes with 4 fans and a thermal sensor (if you buy the plus version). I cannot comment on the build quality but from what people have been saying it seems to be ok. The major problem with this case is the way it looks as some people may like it and others wont.
There are many other cases out there for under £50 but during my research on the same topic these 4 seemed to be some of the best. But like i said its a bit hit and miss as they all have comprimises
Hope that helps