Simple, quality comes at a price. Spine consistency is paramount to consistent shooting and when it comes to tune, (broadhead and otherwise) spine consistency,component fit and alignment is a must. The arrow is more important than the bow when it comes to accuracy. The bow just launches the arrow which actually has to absorb the energy and fly downrange accurately. And to be honest, $100 for arrows isn't that expensive. Look at some of the target arrows out there. They are in the $400 range before building them.
Tfox is one of the best on site as far as any tuning or technical info. He knows this stuff inside and out.
Very true. BUT... Jerry at south shore archery supply will spine test, index, and group arrows by spine, weight, etc to assure that you get the best quality product (and most consistent) possible with whatever arrows you order. I won't buy anywhere else. His prices are cheaper than buying from my local shop and there's aren't tested for anything. tfox is correct. Quality comes with a price. That price just doesn't have to be through the roof