5K can get you a lot of car. Depends why you want a small engine, if its for a young driver then you can get a brand new hyundai with lots of warranty. But to be honest I would go for a golf or a polo, you can get a low mileage 54 plate for that price.
If its economy then i would go for either a golf tdi or audi tdi. (1.9). Even a good ford focus but never driven a focus or owned one so wouldnt know.
Theres so much ou there really, personally i would stick to german cars or the oldshape micr. I know its old but they are great cars. Not the new one to they are rubbish.