Where do you find the lowest-cost sellers of GPS ba? Via sulit, tipidpc, and other online selling portals?

Also, I'm thinking about simply getting the Garmin 205W which is a no-frills GPS device. However, any particular useful features of higher-end Garmin models that makes "upgrading" worth it? I'm also thinking whether the additional screen difference of 3.5" to 5" is HUGE. Any comments about it? I'm eyeing an approximate budget of 12k.