I have extensive experience with the Garmin line of GPSs. I have Garmin units that aren't even made anymore. I'm considering upgrading to one of the super-new nuvi units... maybe that'll be my Christmas present to myself, since all I'll get is coal from anyone else.
Anyhow. In that price range, in a Garmin, I'd go with the c530
. The reason is that it has a high-sensitivity Sirf-Star III receiver, comes with all the maps pre-loaded, and has a sunlight-readable display.
Note: this unit does NOT have "text-to-speech". Text-to-speech is the feature to which you alluded... "turn right 100 feet at Forum Street." The c530 will just announce "turn right in 100 feet." To get text-to-speech in the garmin line, you'll have to step up to the c550
... but this is more than the $300 "tops" price you listed.
I know there are other good GPS units out there... I have never used Tom-Tom or Magellan units. And I know Walmart usually has some ultra-cheap off-brand units.