How much should I expect to pay for head gasket repair on a Renault Clio 1.2l(03)?

I think that the head gasket in my car has gone/is going...One night on the way home from work I noticed a really high pitched noise, so I pulled into the supermarket car park and popped the bonnet open. I noticed that the engine temperature was all the way to the top! The fans were still going when I switched the engine off so it had obviously overheated. Then, being a woman, I opened the water thing not expecting it to hiss and spray steam everywhere... Luckily I was fairly close to home so I managed to drive her very slowly back, where she then drank two whole watering cans of water. Ever since this, I have been having to fill up my water before journeys and I've noticed that when I take the oil cap off it looks creamy. It's about time I booked her in and got her fixed, but after researching, it looks like this could cost at least �400. Is this right? I unfortunately can't do a DIY job,I wouldn't know where to start! I'm kind of pre-empting that being a 21 year old girl with not massive amounts of car knowledge, I will go into the garage and they can baffle me with whatever jargon they like and charge as much as they like, because in that situation I probably will have "Muppet" written on my forehead! So just a rough estimate/ bit of guidance would be fab. Thanks