Unfortunately, most up-to-date unlocked phones are quite expensive
($300+) when purchased without a plan. However, there are a handful of units
that are relatively reasonable.
   For instance, I recently purchased the Panasonic G51U for $219 directly
from panasonic.com (nobody else has it yet). It's primary benefit (indeed,
what gives it "wow" appeal) is it's tiny size -- it's a candybar unit that's
the size of a closed clamshell unit and weighs 2.6 ounces. However, other
than a color screen, world phone capabilities, GPRS and polyphonic
ringtones, it doesn't offer much in the way of features (no camera, no PIM
capabilities, no Java, etc.). So there's clearly a trade-off.
   That said, I highly recommend it if it fits your needs and budget.
Because, so far, it appears to perform quite well. And, frankly, there's
something to be said for a phone that both weighs less and takes up less
space in your pocket than a set of keys.

Rob

P.S.: By the way, a good place to go to research phones is
www.phonescoop.com.

It is not new, but I have a Sony Ericson T616 phone that is about four
months old in very good shape. It is not a flip phone, but it is AT&T,
camera, all that good stuff. Respond if interested.

----
Time for some thrillin' heroics.
----

Also realize that AT&T (at present anyway) do not have a traditional
prepaid plan for GSM.  They have the GoPhone plan which is slightly
different than traditional prepaid plans.

Unless you want to get a subsidy through a carrier such as AT&T
Wireless you're going to pay the *real* cost of phones which as you've
found is not cheap especially for a phone with any sort of features.
You can probably get phones that are not the "bleeding edge" for more
reasonable prices.  For new phones though you'll pay a big premium to
get the best and greatest.
- - - - - - - - - - - - - - - - - - - - - - - - - -