Ok, it's actually a clay extruder but I'm using it for fondant, which is common in the cake world. There was a specific extruder that was recommended on Cake Central, but I couldn't find it anywhere (I didn't actually try that hard).
I found this one at my local Michael's store. I can't remember the exact cost ($25 or $35), but I used a 50% off coupon so it wasn't too bad.
On a side note... did you know that Michael's marks their items up 400%?? That's why they give out coupons all the time... to entice buyers and make them think they're getting a deal! Granted, I don't know this for a fact and can't recall where I heard it, but I wouldn't be surprised. Sadly, we don't have many craft supply stores in the Vancouver area. Michael's is the only one I know of. So, I always make sure I have a coupon handy if I'm going to purchase something pricier.
Anyhow... back to the topic at hand...
The extruder comes with 20 different discs.
Before using it, I washed it out well (it had a bit of an oil smell to it) and greased it up with some shortening before putting the fondant through. I also made sure the fondant was really soft, so I added a bit of shortening to that too. In some of the pictures you can see the fondant coming out a bit jagged so it was probably still a bit too dry.
Overall, I found it very easy to use. A bit of a pain to uncrank the whole thing to be able to add in additional fondant, but not too bad. Will definitely make adding round borders to the bottom of cakes much easier and I can't wait to try to use the hair/grass discs on my next cake!