Vicor (Vicor.com) makes some blocks that take ~300VDC in (You can use a bridge rectifier and cap, or power factor correction ckt if needed) that provide 24V 8A out.
I like radio21's approach. Unless you want to become a smps (and transformer) designer, it is a whole lot easier to use an off-the-shelf module. It's the d**n transformer design and fabrication that really drives up the cost and pain of even a small smps design.
they have complete solutions with different output power
for inputs dc or ac ( 85-265 ).
even they have softwares for that.
I have used some of their solutions.
regards,