Actually, it would be cheaper and simpler to just add a voltage regulator or DC-DC converter to the last MEAN WELL PSU in my list above, to drop the +24v output down to +12v. Then you'd have two isolated +12v outputs, no transformer required.

But truly, it would be best and cheapest to have everything you need in one box that is warrantied by its manufacturer. Surely there must be a PSU out there like that. I've just not found it in the JAMECO catalog, which is where I bought the PSU you see in this dual-PSU SE/30 rig I built:

http://www.flickr.com/search/?q=se%2F30+psu&w=66071596%40N00&m=tags