Sad but true, they are out there charging top dollar for that sort of work, unfortunately you don't know until after. This is just more reason to do what you can yourself, with regard to changing a tyre, if I don't replace it myself, (I do on the little scooter but not on the bikes) I take the wheel off and take that to the bike shop, they only charge for the tyre fitting, which I think is included in the price of the tyre. Hope you get your speedo sorted.