I've been getting charged $100 for my monthly bills and I think that is oddly high. $69.99 plan my a*$. Anyways, what are you getting charged and how does it compare to AT&T, T-Mobile or Verizon? I may switch soon, we'll see.
Your bill should show all charges and what they're for. If you start with a $70 plan, add $10 for premium data, and $10 in fees/taxes/surcharges, you're at $90. Add in another $7 for insurance, and you're almost at $100. It's not all that hard to spend $100/month on a cell phone. When Sprint and other carriers quote a plan price, it's bound to be the lowest, base price. You've got to remember that more will be added, for taxes and such at the very least. I haven't done my own real price comparisons, but I've read that Sprint generally has lower prices than most carriers. Also bear in mind that Sprint still has unlimited plans, something I've read that many carriers are eliminating. (I understand that this is part of the reason the $10 premium data fee is starting to be applied to more than just 4G phones -- to help keep the unlimited plans available.)