Canon USA has fixed prices for repairing the low end consumer lenses, and I've heard that there are price levels set for different types of repairs for the pro lenses.
For a 50mm f/1.4, for example, you can use the canon website to get a repair ticket, pay your fee, and then ship it to them. Unless its a fatal issue, like water damage, they will fix it and return it.
I've always thought that water damage was pretty much fatal to electronics, so I was surprised when my remote Bluetooth microphone used with my hearing aid went thru the washer and the dryer last week, and is working fine. That is still hard to believe. Its nice and clean too.