Mad,
That's a timely question because I actually had that discussion with the driver when he dropped my load - I was inquiring because I needed fuel for the torpedo heater.
No, they aren't the same in price - at the time of my delivery the driver said HHO was about $0.20 MORE expensive than O/R diesel. He gave some reason why it was that way (which I don't recall offhand) ..... but then stated it was kind of a rip-off (like he didn't buy it.)
BTW, the difference in price between regular O/R and premium O/R was $0.02/gal. ...... I figured for $3 (for 150 gallons) it was good insurance.