That leaves me looking at the BA330 which has the same crew of six, a mass of 23mt and a cost of $100m and using it as the basis of a ship design. It would require something like the Falcon Heavy to put it into orbit for another $100m which has the added advantage of providing the ship an engine and fuel storage tanks for free. Not enough to hold all the fuel for a mars trip, but kerosene and oxygen can be stored in lightweight plastic and gravity fed into the upper stage tanks of the FH if we're just going from orbit to orbit. If the complete ship has a 50mt mass we need about ten FH fuel launches costing $1b. But if the ship only has a total mass of 30mt we only need six for $600m. So it's safe to say we could transport six crew to mars from LEO for $167m each. That's too much.
How much would it cost to upgrade the life support to 21? Which still leaves them each a comfortable 15 cubic meters of volume each. Assuming we do that, cost per person goes to anywhere from $38m to $48m.
What about radiation and long term zero g?
Send two ship and tether them together for artificial gravity.