Regulated supplies aren't cheap when you get to that sort of current.
I would use a car battery and charge it up a lot - don't be tempted to use the charger direct as they give a lot more than 12v.
The cheapest option would be a computer power supply. Get a GOOD 500W one - the best way to tell quality is by weight. Just cos it says 500w on the label doesn't really mean much!!!
Most will claim to put out about 18 - 20amps at 12v but take this with a pinch of salt. 10 amps might just be realistic.
Don't pay much more than £30 for the psu.
Diags of pinouts here