The 70W ballast shown is ANSI M98 which I think is not the right one for the Ushio lamps. Those require an ANSI M85 according to Ushio's spec sheets (
http://www.ushio.com/files/Aqualite%200802.pdf )
I dunno I think it's interesting that you can work with 70W lamps but it seems to me the lamps are harder to source, and there are fewer options available, compared to the 150W DE (and they're about the same price, too, I think). 70W and 150W are the same size and use the same sockets so whatever fits for one will fit for the other.
hellolights.com seems to sell the stuff but that doesn't help us since hellolights won't touch a Canadian order (U.S. only).
PS. The 250W ballast shown seems like a good deal ..... not a whole lot of info on the page but I'd assume it's a typical M58.