OK but IMHO there are some proviso's to the advice you've been given.
Firstly, there's no reason why you can't at least get a quote for the repair, if it's more than the lens is worth then fair enough, there's no point. But if it's only replacing the AF switch for example it may well be worth doing it.
Also bear in mind that manual focus is fine if you have a high-end body with a large, bright viewfinder, but if you have one of the lower end Canon DSLRs they're not really set up for manual focus as one of the areas they save money on in the cheaper models is by having a crappy viewfinder. It also depends on what kind of things you're shooting.