I just went through this process a couple of weeks ago for myself. Now I am holding off because the prices are dropping dramatically. All the reviews I read (easily over 50) places the Garmin Nuvi heads above the 2nd place contender which is TomTom. I will be getting the 755T, but for your MIL, in the price range you want, get the Garmin Nuvi 255W. Amazon has it for $215.00 with free shipping. The reviewers love it. Read about it here:
http://www.amazon.com/Garmin-255W-4-3-Inch-Widescreen-Navigator/dp/B0015EWMX8/ref=pd_bbs_2?ie=UTF8&s=electronics&qid=1228356873&sr=8-2