I have to disagree here, a Dargon is nowhere near big enough to send someone to Mars in, it does not have the payload or volume needed.
As far as the dragon capsule goes, much of the research and development of the technology for the crewed version of dragon has already been done. Note that even the supply version of the dragon capsule is designed with a crewed version in mind. And as a result testing has already begun for a majority of the technology required. Also, a crewed version of the dragon capsule would technically be able to make it to mars without enlarging it (although would be INCREDIBLY uncomfortable), the extra space is just that, extra space for more comfort and cargo. the same technologies that apply the the smaller crewed capsule (Currently in active development) should be directly applicable to the larger version with very little modification (Larger fuel tank, extra redundancy systems, more solar panels/ larger battery banks, etc.) Although obvious non critical modification will be made, such as different compartment hatches so rovers can open them.
As Marsman says, it is much more complicated than that. An enlarged Dragon will have to be tested, extensively, this will take several years. And there is no sign that SpaceX are doing this. Without evidence of work this is just wishful thinking on Mars One's part.Like I said earlier, the technology they will be using for the crewed version should be completed by 2015, leaving about half a year to focus on the mars dragon capsule. also 2016 is a supply run, meaning that only the basic components need to be in place. life support systems and redundancy is not required to be in place, and as a result SpaceX can narrow their focus to just getting a bare bones capsule to mars and then have time to analyze data and make needed adjustments before 2021. (this has been the intent of the 2016 supply run all along)
NASA is funding the Cargo Dragon, they are not funding a hypothetical larger version that might put people on Mars.
Funding for Dragon is currently being provided by NASA! SpaceX was funded with putting humans on Mars as Elon’s goal; he is investing some of his own money into the company. Current he doesn’t have to because spaceX is profitable and has external funding. Obviously, I am not Elon and I do not work for SpaceX. But I would be freakin shocked if SpaceX is going to demand a profit or even make a profit off of Mars-One. At cost funding for dragon will be provided by SpaceX’s profits, largely from the NASA contracts most likely, and partially from Mars-One sponsors. If I remember correctly, tv broadcasts for crew selection and training should begin either late next year or early the year after. This should generate a lot of revenue to pay for dragon and the other equipment needed.
Be that as it may, SpaceX still needs time, people and money to develop new hardware. All the signs are they have their hands full developing crewed Dragon, reliable supply runs to the ISS, the Falcon Heavy and the Grasshopper program. They have already dropped some programs becausde they were stretched too thin (Falcon 1E for example).One more thing to note is that SpaceX is not your normal space company. Old expectations should be expected to be broken. Elon came into this industry because he saw a slowing and stagnated industry that needs a kick in the arse. That is what he is doing, try to relate SpaceX to the Gemini missions, not the shuttle missions.