How difficult (and expensive) do you think it is to make puppets, like the ones that were used in TMNT (Teenage Mutant Ninja Turtles), as seen here - -

I'm sure someone will come along with more specifics, but I'd say very difficult and very expensive.

Having said that, I'm sure there's a cheaper method/materials...

You would be getting into animentronics(sp?) for the head area.  The body is made of a special type of latex material.  I would say a small fortune to make something similar. 
Good luck with it, I am not sure if anyone would have the expertise in making such a project in this forum.  I would recommend a special effects forum for movies, they are more familiar with animentrontics and movie prop materials.

However, I could be wrong and someone might have this knowledge on the forum.....you could also search the internet for hints of the materials and design ideas.

Good Luck.....

Daryl H

I have been able to find a bit about it, feel free to add anything else you may know - -

About the Creatures:

The outrageous, fearsome-four green teen Turtles, Raphael, Leonardo, Michaelangelo and Donatello and their ninja mystical master Splinter were all brought to life by Jim Henson's Creature Shop in London. Although the full extent of what they are is a carefully guarded secret - a broad over-view of their creation may be told.

Jim Henson said that the creatures are the most advanced he had ever worked with or created. "Making the Turtles and Splinter was a little tricky because we had to follow the designs that were already in the comic book," he said. "It is a lot easier to put everything you need inside a creature when you are able to start from the beginning with your own designs."

Henson said he thought the reason his projects have been so successful is because of the puppeteers. Led by Creature Shop creative supervisor John Stephenson and production supervisor William Plant, work on constructing the Turtles and Splinter began in February of 1989.

"We first made fiber glass body casts of each creature taking great care to give them all their own individual characteristics," says Stephenson who has developed characters for such films as "Dark Crystal,' and "Return to Oz," plus the NBC television series "The Jim Henson House."

When the body casts were completed, they were given to sculptors to be rebuilt with clay. "They sculpted the muscle structure in the feet, calves, thighs, chests, shoulders, necks, upper arms and then hands and forearms - and, finally, the head and shell pieces," Stephenson revealed. They were then produced as molds to cast the whole body in foam rubber latex - and then painted, giving each character its own distinctive marks and coloration."

Once the foam latex form was completed, complex, detailed work on mechanizing the fiber glass heads began."A system was worked out that had never been done before,"notes Stephenson. "Our electronics computer expert, Dave Housman, developed new technology utilizing radio control, computerized speed, power and simplicity of operation."

In the past, a close-up of an animatronic's head, Stephenson explained, has required several puppeteers and much rehearsal to produce the required expressions. For the Turtles' movie, a way had to be found to enable close-up Turtle heads to lip sync fast and efficiently combining all the extreme cartoon type facial expressions found in the comics.

With a talented array of over fifty team members consisting of supervisors, designers, sculptors, mechanics, costumers, seamstresses, plasterers, painters and an electronic computer expert - all working together - Henson's Creature Shop was able to complete work on the Turtles and Splinter in a very short eighteen week period and have them delivered on time to the North Carolina Film Studios for the start of filming.

The movie's chief puppeteer and second unit director was Brian Henson (son of Jim Henson) who had the important responsibility of directing many of the stunt scenes and also making sure that all the puppeteers perform their characters to the very best advantage.

Before filming began, Brian ran rehearsals with the performers and the characters so he would know their performance capabilities and could be of important assistance to director Steve Barron during the actual shoot. One of his favorite scenes, he said, was where Raphael carries the unconscious April into the Turtles sewer' den. "There's a nice feeling between the two of them and it is a lovely sort of image to see these four huge Turtles and a giant rat living in a home in the sewers under New York City."

When aspiring puppeteers seek his advice, Brian says only that they must regard puppeteering as a creative craft you have to work at and train for so that "you can finally get your hands to do what you, instinctively want them to do. And once you are there performing, you must have the ability to pull yourself up and out of yourself and into your hand."

A step further, he says, is when you learn "to perform the character while looking at the character only on the monitor. Then you are just concentrating on the screen character - and that's the character you really bring to life - without thinking of your hands. The effect is much more believable and more magnificent."