If you want a good quality, comfortable and cheap pair of jeans then I’d recommend finding your nearest GAP Outlet store. They don’t have the same narrow/skinny/shitey things like in the normal store they just have a nice selection of slim/bootcut/loose fit jeans and can usually be picked up for around £20. Mine tend to last the best part of a year and that’s wearing them most days and they are so comfy (currently sitting at work in a pair of premium loose fit) and they do absolutely loads of sizes.
I usually struggle for jeans as I hate tight fitting ones and my thighs are pretty big, the GAP Outlet loose fit are the only pair of jeans I have managed to find for years that actually are a loose fit and are really soft whereas I find Next jeans like cardboard everytime you put them on and nowhere near a loose fit!
Also if you sign up to their emails they have sales and offers pretty much every month giving you more money off, snap up some bargains!