This was a lesson I learned the hard way with my first startup: Be cautious about how much you undercut your largest competitors unless/until you have deep pockets and/or unless you're very sure that their economics makes it impossible for them to undercut you on price, because the more you undercut them the more you're inviting a price war you can't win without deep pockets the moment they perceive you as a threat.

When trying to enter an established market to compete on price as your primary differentiator it's often better to keep your margins higher to start with than offer the steepest cut you think you can afford, and then drop your prices slowly as you build up volume and a war chest.