Now that we don't have to worry about pre-ban/post-ban parts combos, where is a good place to buy a lower so I can build my own collapsible stock shorty. I never considered this before because of the crap involved but with the sunset of the so-called "ban" I am anxious to do this before some dipshit in Congress decides I shouldn't. I am guessing that I will have to do the FFL/From 4473 thing on the lower and the rest I am free to buy as I please. Your input please.
Finnbear

i got the stripped lowers from eagle firearms (www.eaglefirearms.com).
i got the lower parts kits from armalite (www.armalite.com).
i have a 6-position collapsible stock coming from legal transfers (in the ee).
i got 10 30-round labelle mags from surfit (in the ee).
i have an order in to model 1 for the upper (www.model1sales.com)

yes, the lower must go thru an ffl (4473). the rest does not.

After poking around here a bit I see mentions of lowers from RRA, Eagle, Olympic, etc. What are the differences if any?

There are almost no differences in lowers from different manufacturers, as long as they are Forged lowers, you are getting a good one.  Many are forged by the same foundry and then machined by various contract machine shops who do the work for the various names stamped on the lower receivers.  You may find small differences in some lowers over others, and I am talking .001-003" of an inch in different locations, while not much of a difference, I have had to dremel very small amounts of material from different manufacturers lowers and uppers to make them fit correctly.  This is no big deal if you understand basic mechanics or have machining experience.  Most people can use a dremel, just think carefully about what you are doing and the best of many ways to do it and you will be o.k.  A good example is a RRA lower onto a Bushy upper, the lugs on the rear of the upper fit too tightly into the lower and it will not close.  Upon close inspection you will see a slight raised boss at the top of the lugs on both sides, just try to close it gently a few times and you will see where the interference is, then lightly dremel a little off each side until it is a perfect tight fit.  Use aluminum black to clean up the dremel marks and it looks and fits perfect.  Caution: a little at a time.