My dad was quoted around $690 for a map update on his 3yo Merc. In comparison $290 for 3 yrs seems a good deal; but yes, I agree, overall, it's a rip off.
I have been using the Tom Tom Go app on my Android based phone for around 8 months now & am very pleased with it. The large, high resolution screens on our smartphones nowadays give you a pretty decent display.
Maps are downloadable, so the app works fine even when offline. For current traffic info you need to be online, naturally.
It's a subscription based service costing $9/mth, or $30 for 12 mths. You can trial it for free, as they give you 70 kms/mth at no charge.
I was lucky enough to pick it up on a $15 for 12 mths special they had back in Oct last year.
All updates, maps, speed cameras etc, are included in the subscription.
I love the large screens of the built in GPS systems but the cost of updates is a major negative.