I have a 55 reg 1.6 Vauxhall Astra that wont start!

I drove it fine this morning to nursery but then when i came back to it it wouldn't start. I turned they key and there was nothing at all, no sound and the engine didn't even make an attempt to start. Some of the dash lights came on but then went out again. I tried to lock it and unlock it to see if that made a difference but no. When it was locked the hazard lights on the dash inside flashed but not on the outside.

Im going to have it towed to a garage in the morning but would just like to have some idea what it could be and the kind of expense im looking at.

Thanks