Hello everyone I need some advice on this one. Now 3 days ago I noticed my engine is making a knocking or ticking noise coming from the valve cover. my friend said my Lifters might need adjusting or replaced.

So I take it to a mechanic and test drove my lifters have to be changed and that my timing belt should be changed and the belt possibly could be bad which is creating my lifters to go out and the noise is this any truth behind it if so is it a easy fix? costly?