IMO even for practice you need to do it on leather, nothing else will work quite the same and you won't learn the feel of the leather.
Now for practrice leather you don't need expensive brain tan - get a hide of Crazy Crows German tan, they sell seconds and if you have a business license they will give a discount. I use a fair amount of the German Tan and it works just like brain tan but at a much lesser price. BTW - the seconds are just as good quality as the firsts but they have an extra thick neck section - I keep this part for moccasin soles or other projects I need a thick piece for.
http://www.crazycrow.com/mm5/merchant.m ... 45-100-000Current retail is $63.00- these hides are great for making Indian goods including pouches and moccasins ( I wear side seams a lot and the bloody things wear out so fast I seldom use anything but GT and the plus is I always have the extra thick section for an add on sole which extends the life quite a bit. Plus tenderfooted folks can use the thicker section for inners soles as well.)
also I recommend pre-stretching it - this will keep it from bagging while working and also adds a bit of footage. They say don't dampen when stretching, but I do and it works fine. The hide will be a bit stiff after drying but it softens up with little work and actually I like it a bit "stiffer" for quilling or beading.
BTW - William Orchards, IMO must have book, on quillwork is available as a free download via Google books.