quick answer…YES!.
Longer answer…Madrid is not cheap perse but depends exactly what you want out of madrid. For 900 euros you can rent a very nice flat, just check areas, obviously some are more expensive than others.
Petrol is cheap, insurance…depends on your circumstances. Going out can be pretty cheap certainly compared to Britain (dont know where your coming from).
Put it this way even though the cost of living may not necessarily be that much lower that other EU contries in certain respects the quality of life you can have more than makes up for it. Eating out is fantastic and generally pretty good value. Daily menus in restaurants and cafes start at around 8 euros for a starter, main and desert (or cafe).
The flat you rent may well have a pool, gym and social club areas for that 900euros. Life in no doubt different over here.
Hope you find what your looking for.