Many of the Philips models, such as the DVP-642, can be easily hacked with just a numerical code entered from the remote, many of them have built-in PAL converters so you literally can play any disk from anywhere in the world, and many models, such as the DVP-642 can be had for under $50.
To get the code for hacking the player, regardless of which player you get, check out
http://videohelp.com/ . They have a section which lists players by make and model, lists compatibility features, and lists any hacks they have available for that model.
If you read through the reviews on Amazon.com, a reviewer will sometimes indicate if a player can be made region free and if it has a PAL converter built-in.
The DVP-642 is a bit of an older model now, but it has been a while since I have looked into region free players.