It's hard to say how much these development vehicles would cost. Elon has said Starship development is expected to cost at least $5b. Long term, SpaceX have aspirational goals of $2 million per Starship launch. This is plausible providing they fly lots of flights with each Starship and booster. The Raptor engine powering Starship and Superheavy booster may be able to fly 1000 times before a major overhaul/retirement. Currently Falcon 9 costs about $50 million to customers (about half the nearest competitor's pricetag). The marginal cost of a reusuable Falcon 9 flight to SpaceX is about $15 million, with $10 million of that being the second stage which isn't reused. That demonstrates just how important full reusability is. Starship may eventually have a cost of less than $50 per kg to low earth orbit. Compared to ~$20,000 per kg to LEO for the Space Launch System (SLS) being developed by NASA which is the closest comparable system. The Space Shuttle was about $50,000 per kg to LEO.