Depends on what you are building the bike for. Throw away training bike? Long term keeper? Something to sell fast?
These questions and those not listed affect the answer to the question you posed. RevTech is a brand with lots of baggage on the negative side. They are not robust. So if you what this bike to last a long time before fiddling with it, and you may be gonna work it hard, invest in a more robust power plant, like S&S or Ultima, etc.
If you want a replica engine of some of the early models, you need to find a custom performance shop that builds knock-offs. Go see them.
If you want cheap in order to turn the bike over quickly, RevTech may be a good fit.
I would not buy a new HD engine for a home build. You will not see a return on the investment, and HD will not stand behind the engine any longer than the original warranty if that even (if you modify it, it's yours!). A used engine or rebuilt one (from a known shop) may be a reasonable deal.
So, basically you have to evaluate what you need the engine/bike to do, and then make decisions from that. There is no simple answer that is worth having.
TQ