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I thought I would add my 2cents worth on this subject.  Getting along just
great at my house for the last 6 years with CD, I have converted to using
corn starch and rice flour almost exclusively in my cooking.  When I started
out, I read all the recipes and bought lots of tapioca flour, potato flour,
potato starch, sweet rice flour, bean flour, .....

Finally, I have decided for myself, that cooking is simpler with fewer
flours.  I bought my own flour mill and mill rice flour about once every 2
months.  Then I buy corn starch in the regular grocery store.  Almost every
recipe in the GF cook books works well with these two inexpense and easily
obtainable materials.  I use the corn starch any time the recipe calls for a
starchy substance such as tapioca or potato.  I get very good results with
minimal effort.  I think the greatest win is using my own mill on the rice
which gives a much finer flour than you can buy in the store.  I never notice
grittiness.

Just my 2 cents, from a lazy but good cook.

Debbie in Colorado