I use Briess Bavarian wheat DME which is 60% wheat.
I'd think a mere 30% wouldn't produce a very wheat-like beer. Can you do a partial mash? If not can you get the Briess DME?
I gave up on buying the bulk of my ingredients from my LHBS as I decided to order it once instead of going in and they stuck it to me BAD! And when I called him on it it took quite some time to get it fixed, and he still charged $1 more, plus charged me the higher shipping fee, which went against their policy. Now I just buy my grains from them since they'll sell exact amounts.
I prefer to support small/local business, but now I just deal with MoreBeer as they are comparable in price to others, but offer free shipping on orders over $59, which I always do. I certainly don't want to suggest you no longer support your LHBS though.