I think the most viable thing to do would be to put your money towards building a geothermally powered unground habitat that is close to a large water source, and have a really good water purification system to filter it.

Also possibly use fibre optic cable to funnel sunlight in to grow plants which hopefully produce food and oxygen. Although safer bet would be to have enough power for internal ultra violet lighting and be able to split water molecules into oxygen and hydrogen, who knows if we'll somehow managed to block out the sun as well.

I've been thinking about this for a while, if anybody can lend me some large scale industrial excavation equipment, I'd really appreciate it c: