My speedo isnt working in my renault clio 1.4?

My renault clio 1.4 speedo stopped working, i only bought the car on monday it was working fine, untill i got near my home i had only been driving the car for about 1 hour and it stopped, i took it for a drive again today and it worked untill about 10 mins into my drive and it dropped again, dose anyone know whats wrong with it? and how much would it cost? Thanks