As of this post, there's really only a few releases that are worth the amount that you would have to pay.
$25.99 isn't a terrible price for 14 episodes:
http://www.amazon.com/Teenage-Mutant...+ninja+turtles
And $3.59 isn't a bad price for two episodes:
http://www.amazon.com/Teenage-Mutant...+ninja+turtles
Finally, $10.76 isn't a terrible price for the Turtles Forever movie (then again, I think you can find it at Target for like $9.99)
http://www.amazon.com/Teenage-Mutant...urtles+forever
So I'd say if you don't own ANY of the dvds of the 4Kids series, just get the Turtles Forever movie for now and enjoy the Nickelodeon series.