The mars homestead project sees itself as a better use of resources than the design reference mission. This is my argument for why you send a dozen or more at a time rather than a mission crew of 4 to 6.
Assume we have a FH capable of putting 53mt to LEO for $100m, which can also preposition a red Dragon lander in mars orbit for $150m capable of landing seven on the surface of mars.
Bigelow has a BA330 with life support for six and a mass of 23mt. Assume it is the basis of a 50mt ship that costs $250m unfueled to LEO. This provides an abundant 55m3 (cubic meters) for each crew member. Using a 300s kerosene engine this ship would require about ten FH fuel missions to reach mars costing about $1b. We should also preposition supplies on the surface of mars. Let's say four red dragons for $600m. Add a crew dragon launch for another $60m. We round up $1.91b to $2b for incidental expenses.
So this configuration gives us a total cost of $2b to send six to the surface of mars with supplies.
We could pack crew into as little as 9m3 but if life support for a BA330 were upgraded to 21 they would still have an abundant 15m3 per crew. I don't know what the cost of upgrading life support might be (haven't found a good reference on current systems costs.) Let's say it's $20m.
We need to preposition two more red dragon landers for an additional $300m and add two more crew launches to LEO for $120m. The fuel launches don't change because we haven't added enough mass to make a difference. So let's round up the additional costs from $440m to $500m.
So for an additional 25% cost we get an additional 350% of crew to build our colony on mars. We should send two of these ships with 42 crew. We need to stop thinking small. Many hands will make the workload lighter and provide each with more mutual support. It will make the colony more likely to succeed. Overall it will lower risk.
Update: we can lower cost even more if we have an extended dragon putting 21 to LEO in one launch of a FH. This upgrade would only come when we have more mars missions. This passenger shuttle may actually be cheaper than a single dragon since it doesn't require as much capability. Because of the greater difficulty of landing on mars we continue using the seven passenger red dragon landers.
Elon says he hopes to get the cost down to $500k per person. If he gets anywhere near that and you combine my settlement charter with it you've got the greatest land rush humanity has ever seen.