Is it cheaper to buy a new sat nav than upgrade the maps?

I am finding my sat nav map seems to be quite out of date, eg doesn’t have latest roads added to it and places where the roads have changed.
I’ve looked at getting a new map from Garmin which is £79GBP or something but there are Garmin sat navs on Amazon for less than this!
My Nuvi is only about 2 yrs old and is fine – am I totally missing something with the maps?! Is there somewhere to get them cheaper?

Well, Garmin would be the only place to get the map updates. If you can find nav’s that are cheaper than the map updates, and from a reliable seller, then get the new nav, but it’s weird that the updates cost more.