In the manufacturing sense, HD-DVD media is currently much less expensive than Blu-Ray to produce. I don't think this really tips the balance much in the HD-DVD vs. Blu-Ray war, but it's worth a note. All new technology is outrageously expensive when it first starts up but improved manufacturing methods and competition drop the price over time. Anyone remember the first VCRs that cost around $5,000?
So, why the cost difference in production? HD-DVD manufacturing can generally use a standard DVD production line, with some minor modifications. These mods are only 1/10th of the cost needed to ramp up a Blu-Ray manufacturing line, but again, this is likely a short term difference. Additionally, Blu-Ray discs require a film layer made only by Sony. That might be good for Sony in the short term, but bad all around for Blu-Ray if you ask me.