Green Mountain makes octagonal standard caliber blanks.
http://www.gmriflebarrel.com/catalog.aspx?catid=TaperedOctagonBlank414011"Long
But unless you can thread and fit that $100 blank yourself, it is all going to come out like that Clements custom job of $500. For $400 he is going to have to turn and thread the shank, justify the threads so a flat comes out square on top, cut the shank to length for proper cylinder gap, probably draw file, then polish the barrel so it looks good, install an ejector rod stud at a funny angle, install a front sight, cut to length, crown, and blue. Phew.
The AWA octagonal is $700 - $800 and you will not get out cheaper than that unless you can do the work yourself.