How often do the maps on the Garmins get updated?

if they're free or not depends on which of the things I've been reading abut updating maps is true or not - one thing I've read says the first one is free, and after that, you pay for them, other things I've read say you get a free update only if you bought a unit after the release of the new maps and your unit has the old maps on it. The price for the map set in the Nuvi is $75. Considering what I paid for my 350, and the use I've gotten out of it already, I will not mind springing for the $75 when the time comes.