I used Lam Birch for years out of my Hill.
Before finishing, straighten using mild heat and a glass bottle (burnishing). The shafts shouldn't be so hot that you can't handle them (too hot and the glue will stress).
Do this twice over a week, bundling tightly together once finished.
Once straight, cut/finish/seal immediately, and fletch at your leisure.
They should stay straight if you store them properly, and if sealed well will not warp under field conditions (i've used them chasing moose in rain for ten straight days with no problem).
Spend the money and deal with a Mom and Pop shaft supplier. You will be happier than dealing with a larger outfit where you may have to junk 25% of what you buy.
Quality does vary supplier to supplier. Look in the sponsor's classifieds.