The cheapest one that I know that has TTS is the Garmin Nuvi 350. Its going for $350 until the 22nd from
Costco. VERY nice unit if your looking for spend around that much on Navi. This has the newest SiRF III reciever, is less than an inch thick, has TTS, MP3 player, and also has optional traffic nav, and also has Garmin's mapping software interface, which is considered by many to be the best.
Other, more expensive Nuvi's add features like bluetooth (so you can pickup your cell through it like a handsfree kit, but with no earpiece), and FM Transmitter (So you can hear your GPS/Call through your car's speakers)
I don't travel that much that I need an expensive navi unit, which is why I bought the Mio. I bought it for those once-in-a-while roadtrips, those times you take a wrong turn and end up in some town you've never been too, and those times you follow a friend to some place, but you have no idea how to get home.
For the price, you can't beat it. Its no Nuvi, but its pretty close for half the price. It has the same SiRF III reciever, same thin profile, can play MP3s. Maps are kind of old (about 2 years old), and it doesn't navigate around jug handles too well, which Jersey is littered with, but for the price I cant complain too much. I also found out that CompUSA has them on sale for
$149 this week, if you have one that isn't going out of business in your area. (They have closed/are closing down over half their stores, and those stores probably wont honor this deal.)
If you plan to use GPS alot (Travel a lot, or need to travel for work), and have some more money to throw at a GPS unit though, I'd highly recommend the Nuvi at the sale price.