How much would it cost to get a Flasher Unit replaced?

[jesta]

My Honda Civic no longer flashes when I indicate. The light just stays on when indicating. My mate believes the flasher unit is broken causing it not to flash. Roughly how much would it cost to get replaced at a garage? Went into Halfords to see how much the part would cost, the guy said it would cost roughly £12 is it a easy fix if so I might as well have a go at trying to fix it myself.

Thanks.