I guess it really depends on your definition of affordable.
When I started looking into it, I chose a White Oak Armament 6.8 barrel and planned on getting the headspaced bolt with it. Your talking about $336 for those plus shipping. The other parts are interchangeable.
So, whatever lower assembly you want ($400 to 600), an upper ($100 to $200), gas block and tube ($40ish), a forearm (cheap to $250) and a carrier group ($65).
You could get into a good 6.8 rifle for $900 to $1200.
Too bad you sold your AR, you could have converted it over for $340.