At the high amperage you get about 4 volts drop from the Cree's. So why not use 30 of them or so in series, and run them right off 120v with a rectifier, capacitor and a resistor. There's alot of variation in them so you can't get a precise voltage drop, but it should average out... If you get close enough to the 120v or whatever, you wouldn't need a ridiculous resistor (the more wattage you try to dump with a resistor, the more heat and larger it needs to be).
Would be about $150 in LEDs, if you use the XPG-s you could get about the same output as 4x65watt CF's, so enough for 55 - 100 gallon tank and be in the 'ridiculously high to high light' range.
You don't really need to use a buckpuck for these applications if you're using AC. We don't really care about efficiency, except perhaps to minimize heat from resistors, but proper design can minimize the inefficiencies without having to resort to a buck driver.
Alternatively, if you wanted to work with low voltage, you could plop $60 on a 12v power supply and do a similar thing, or plop $20-30 on a laptop power supply (~24 volt).
I'm still convinced you could do this all on 120v with $10 of components... For setups that are good for less than 50 gallon tanks, where you want to use less than 30 LEDs, I think you could just use a transformer to drop the voltage to whatever you wanted, then rectify it. Only need 1.5 amps from the transformer, so don't need anything terribly beefy.
XPG's can be had for about $5 or $6 individually. I'm sure you can get a volume discount. I don't think I'd use a lens on them since I believe the output is in a lambertian pattern, which is pretty much what we want anyways, but 30 lens's would only be a couple bucks total anyways.
This bridgelux is pretty sweet. 10% more lumens from the same amperage as 4 XP-G's, although it costs about the same as 4 XPGs. Realistically, you're right, I don't think the light output would be even enough for one of these to fill out. One of these really could light up a 10 gallon with a good amount of light. I have the same lumens on my high light 10 g. 6 or 7 of these on a 55 gallon would be kinda weird...