My last purchase was a 5-door 1.25 Picanto with c. 20k on the clock for this sort of budget.
You can get them still in warranty for 3-4 years, and given the size of the car they're actually pretty nippy. More so than the 1.6 Diesel Golf I use at the moment.
What Picanto model was that out of interest? On the site, there are various options.