You can make the halters without much trouble. I tried to make the 22 foot line, and I had a very hard time finding the same feel in the marine rope. I made one, but the original Parelli one is still my favorite. Same thing for the 'carrot stick'. I made a "turnip stick" but it doesn't have the same weight, feel and flexibility as the original and hardly ever gets used.
Funny thing is, I don't do Parelli. I play the 7 games with my foals, but that's it. But those tools are the best I've ever found. I just found a replacement swivel snap to fix the clasp on my line and I just ordered a new Savvy String.
It's kind of expensive to purchase in the beginning, but IMO it's worth the cost. Current price approximations are:
22 Foot Line $57
Carrot Stick & string $62
Total $146 plus shipping
That's not a real expensive Christmas present or can even be pretty reasonable if you split it up between family & friends. Otherwise, I'd recommend buying stuff 1 piece at a time and collecting it all that way.