Replying to a two year old post, but the cost of Raptor engines is reported to be less than $1M, perhaps much less, and they are being built by the dozens while being greatly and continuously refined. Hard to see the old school economics winning out here.
The cost of the RS-25s being used is around $70M each according to one NASA report/audit, but that figure may not include all relevant costs. The engine "set" is what is around the half billion dollar ballpark.
All seemed so very retro.
Totally throw away boosters, totally throw away booster - including the 4 Shuttle main engines at $500M each.