Transferable M16 machine guns and estimated market values:
RLL $15-18k
RDIAS $27-32k
RR Non-Colt Cast AR15 Conversion $17-19k
RR Non-Colt AR15 Conversion $18-20k
RR Colt AR15 SP1 Conversion $18-20k
RR Colt AR15 614 $22-24k
RR Colt M16 $22-24k
RR Colt M16A1 $24-28k
RR Colt M16A2 $28-33k
RR Colt M16A2 Commando $33-38k (Marked "Auto" instead of "Burst")
Websites to watch for good deals on machine guns:
http://www.sturmgewehr.com
http://www.atfmachinegun.com
http://www.autoweapons.com
http://www.impactguns.com
http://www.subguns.com
http://www.onlythebestfirearms.com
http://www.davidspiwak.com
http://dealernfa.com
http://www.gunbroker.com
http://www.nfasales.com
http://www.classiiidealers.com/
http://www.westernfirearms.com/
http://www.collectorsfirearms.com/class-iii-full-auto/
http://www.urban-armory.com/
http://www.ar15.com/forums/f_7/118_NFA_Firearms_andamp__Parts.html
Website that tracks machine gun values:
http://www.machinegunpriceguide.com/