The major benefit is that the return vehicle does not have to be sent with the initial launch. Later supply missions could include return vehicles and replacement colonists so the original members can return to Earth. I think a longer mission would be easier to sell to the public. This is not a huge investment by today's standards. It could be founded with a high profile IPO and invest the proceeds in Aerospace and Tech companies.
Ongoing revenue is generated by broadcast rights, and selling Martian real estate.
My original suggestion was for a minimum stay of 6-8 years. There is a big difference between this and staying forever. The major benefit is that the return vehicle does not have to be sent with the initial launch. Later supply missions could include return vehicles and replacement colonists so the original members can return to Earth. This is not a huge investment by today's standards.