I agree, there are lots of free boot disks. But our poster wants to know about value, not availability.
I have seen some of these wonder disks, and most are simply compilations of lots of free utilities with a slick menu. Compiling these boot cds obviously took time, time that you may find better spent in other pursuits.
One such disk I saw had over 200mbs of boot utilities, from mem tester, burn in tools, partitioning tools, network conectivity with autodetect for a massive list of NICs, and even manufacturer low level drive tools.
So are they worth five or ten bucks most of these people want? I don't know, you make one while I go enjoy life for four or more hours, then you tell me.