I'm a bit confused !!
First you say you can't change a tap washer, about the most simple of jobs then you say you can change the whole tap for £30.
Change the tap then. If you can find a proper kitchen tap for £30 that is not imported from god knows where, that will leak again in no time good luck
Yes if it's a washer type tap.
Some taps have cartridges, if this is the case you will need to remove the inside bit as shown in vidio and take it to a plumbers merchant. A local plumber should only charge about £40 to repair it.
As it's a combi you will need to replace both washers to be sure.
If the hot water is coming from a cylinder in the airing cupboard there should be an isolating valve on the cold feed which enters the bottom of the cylinder. Turn valve off and open hot tap, water should stop. If the tap still drips it will be the cold tap. Close the main stop cock in the road...