I have collected all the big parts to do my 3-4 retro's with the exception of the long awaited NDS lower and the lower parts kit.  I realize I could try to collect all the correct parts over a period of time, but not sure it is worth the effort.  I am only going to shoot these rifles.  Is a DPMS lower kit a good way to begin this project?  Seems like you can get all the springs and pins and such at a pretty reasonable cost.  I do realize that some of the exposed pins would not give good credence to a good retro build....  I do like my RR trigger in the M4 I have, but in their adds they do not give enough information to understand if all the parts needed will be included for the 180.00 they are asking.  I am sure this is a commonly encountered problem, but it is one I have been stewing over for quite some time.  Any guidance around this issue would be helpful.  My retro will be a 1969-70 era M16a1.
TIA

My Semi-retro is built on a DMPS lower. It runs and looks fine;

You should take a look at RB Precision on the Industry Forum. They sell a lower parts kit for $51. If you don't need the A2 grip the LPK would cost you $50. The folks at RB are good people and a pleasure to deal with.