renualt clio 1.2 1999: speedo not working and false fuel reading?

hi there my renualt clio speddo is not working at all it used to work when the lights were off but wont work at all now also my fuel is reading half full when it is empty every so often it all works fine for couple minutes then goes back to normal. The garage said it could be the sensors below the battery which i think control the fuel pump and the fan but i dont want to spend £30 pound if that is not going to fix it. can anyone help thanks.