Hence the advice "charge more". Never try to compete on price, it's a race to the bottom that commodifies your work, and you're competing against people able and willing to work for a pittance. Be strategic, be viewed as strategic, and price accordingly. Also, consider a hybrid with a fixed-price base (esp. w an initial "discovery" phase, priced on its own), and explicit provision for time and materials overages. Mostly, figure out what works for you, and do everything in your power to deliver value for your clients.

I say all this having used a few different models over the years but also presently engaged in a long-term (well-paying) hourly contract that's honestly been a welcome break from the sales/marketing/bizdev aspects of consulting.