(if you get a car on contract hire, do you have to pay a couple of K up front as well?)
I reckon you're overestimating the additional maintenance the old car will cost you.
Also you appear to be saying the 15K price of the car is important to you - surely it's irrelevant, it's what the car does, not what it costs which is important.
Back to a point I made a couple of weeks ago about you only considering 'banger a month' and shiny new, and you said you wouldn't consider the mid-point worthwhile. I still reckon you're underestimating the cheap end of the market. Even really quite cheap bangers (ie 500 quid or below) last well over two years if chosen sensibly.
So do what you said you wanted to do : get an old golf GTI, and wait till somebody makes a car you want again.
(you're not doing well on soft tops at the moment, are you? no good words about the 306, and you won't have another beetle...)
cheers, clive