Well I had a quick look while I was eating lunch and it seems you are somewhat limited in choice, £4k will get you a 2014 Ford Ka with 45k on it, or a Kia Picanto, or a Corsa etc. Obviously at 7 years old, you need to make sure you are buying something mechanically sound with a good service history. No bells or whistles on either of them either, as expected really, but I suppose it is like when I go abroad on holiday, I tend to rent a whole villa rather than taking a cheaper package deal to the same destination overall, and staying in shared accommodation with shared facilities. Yes I am spending quite bit more for the same time away, but my overall satisfaction of the time is greater and I tend to enjoy it more.
It is all a balancing act to find what is acceptable to "you" and for some that will be a low end car, that is newer, at a higher expense for piece of mind, or even just enjoyment.