Don't go rushing into anything, if the car is running fine just using a little too much oil, dont scrap it, wait till it dies.
Mayonnaise like stuff on the rad/oil cap, blue/white smoke from the exhaust (when up to temp) and lack of power may all point to the head gasket being damaged.
But the mayo stuf could just be a little bit of moisture in the system, from the cold weather, white smoke from the exhaust could be the choke on the car before it hits optimum operating temp.
Head gasket if you get it done by a garage would probably be about £500 I would have though, mainy labour as the head has to come off and may need to b skimmed for the new gasket.
Your best bet, is to give it a little service of your own, get a new oil filter and seal(£5), sump plug(50p) and drain and change the coolant. Also change the air filter and you have done it all then. These car's have really simple engines and to do that it will be straight forward and fun TBH.
All I'd say you would need is a haynes manual and it will guide you through it all easily.
HTH.