The cost per colonist goes down the more you send at a time. For survival the martians will need to establish farms and industry that requires more than a few hands. This is why missions of about four are too small. We can send more and should. I propose a dozen on the first mission ($2b) and three dozen ($3b) on the second.
More mass means more cost so we need to keep the mass, especially of the first missions, down. This is why, existing launch systems are large enough to go now. Falcon 9 can put 13 tons in orbit. The Dragon will have life support for seven and weighs less than 5 tons but it doesn't have enough internal volume for a long mission. So a low mass inflatable (under 2 tons, possibly from ILC Dover) should be added leaving about 6 tons for 6 crew and supplies. This would cost about $100m each and we should send two. By keeping the upper stage (or better yet, integrating it with a dragon which is not going to be landing anywhere) it should be refueled in orbit and will have plenty of delta V for reaching mars orbit. It could send 22 tons to mars orbit so will have plenty of margin for a 13 ton stack. Refueling in orbit, an enabling technology we should learn sooner rather than later, will cost a few hundred million. A dozen colonists will require three landers (cost $190m each) waiting in mars orbit. So the first dozen to mars will have a mission cost of less than $900m if done this way. However, this does not put enough supplies prepositioned on mars. I recommend more (at $190m / 2500 kg.) So let's say this first mission costs $2b to put a dozen colonists on mars. That's 3 times more colonists for 3 times less money than the Mars One mission (9 times more efficient.) We still just send one lander with four colonists for first landing. We just don't have to wait 26 months for the next eight. They will stay in orbit for several weeks while the first four determine survival potential. Those eight could return to earth (but it's unlikely they will have to) or the ships could return to earth empty for their next crews. The only thing missing at this time is the lander, which Mars One has on its schedule for 2017 but SpaceX has not yet tested. Please focus on this Elon! It makes everything else possible now.
Assuming the MCT is not ready in 26 months after that first mission we can still send 3 dozen on the second mission in a better ship. This ship would definitely integrate an upper stage with an inflatable habitat. It doesn't have to land like the MCT so is not a difficult engineering challenge. We would need 9 landers waiting in mars orbit (9x190 = $1.71b) but would not need prepositioned supplies on mars since the first dozen colonists should have enough production to cover that. Massing about 40 tons it would launch on a single Falcon Heavy and should retain about 10 tons of fuel once in orbit. It would require several FHs to fill up its fuel but total cost should still be less than $3b.
So in 26 months we could have four dozen colonists on mars. The first mission could go in just a few years from now. Total cost for a new world worth trillions? ...$5b. They could still be reality TV stars, but being members of the settlement charter they don't have to be slaves.
Actual cost to do this... $300m (the cost of putting a leasable ship in orbit with profitable shakedown cruises around the moon.) What am I saying? We should build the 40 ton ship for our second mission first and make it earn money in cislunar space. We still use the 13 ton stack for our first mission, but our ship for the second mission could pay for all of it. The lease potential for lunar tourists should be up to $3b a year (assuming up to $10m profit per tourist... Tito paid $20m and didn't get to go around the moon.)
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