Chartplotter question

[msmith10]

I think this is the topic forum for off-topic (not A-4) questions. If not, I apologize. This is my favorite boating forum, though, so I'm going to post this question here.
I am looking for a new low-end chartplotter for a friend. I love my Garmin 172C-- intuitive, simple. It came without any built-in charts, and you "unlocked" charts from a CD for desired areas and loaded them into the unit.
The new Garmins of comparable price (under $500) come with "built-in worldwide basemaps" but I can't tell what this means. Are these detailed navigation charts? Do you need to purchase charts separately?
I'm sure some of you have similar units (Garmin 420, 421 specifically look appealing) and can help me figure this out.

[rigspelt]

Base maps are not for navigation. If the Garmin unit does not come with preloaded BlueCharts, then you'll need to purchase them.

[JimG]

There are lots of 172/182s on eBay for less than $200...

[nickmerc]

I bought a Garmin 441 this summer. It had the coastal preloaded maps. I got it for about $450. I have been very pleased with it so far.