Be patient. If you want a specific model/colour say a yellow sporting then your limiting yourself and probably pay more but otherwise a cheap car will apear.
If your in the market for a car under £1500 then you need to go private.
Whats advertised by the trade for £1500 cost them £900
Notice the scappage incentive has played havoc with old car prices, the supply of 10 year old cars has much reduced, there are fewer cars available.,
If you want a punto best look for an 02 plate that wont qualify for scrappage,
buy private, keep £250 back you saved more than that buying private and if necessary spend that on getting everything right. See what prices they are national on autotrader, but search in local papers , piston heads and all the free sites no one ever looks at. Be prepared to travel 20 miles to look at a car,
Once bought - Change plugs, filters and stuff wont cost much and if you dont need to spend anything else then you can spend on a sub , and new head unit.
Dont blow £900 on alloys for a car worth little more.