Self driving cars do drive themselves. They are completely autonomous, there's no need for a driver in the seat. The reason they're using drivers now is because they're just beta testing it and it's still not legal everywhere (although it's not illegal either) (except in Michigan where they just passed a law that it's legal).
As far as the cars costing more than $30k, it doesn't matter how much the car costs (to an extent, obviously one car can't cost $1 million as they'll never make a return). The key is that it's a "capital" cost. Meaning you pay it once, and then everything the car makes goes back to making back that capital cost until the cost of the car is paid off. Then once it's paid everything after that is profit. Current full time drivers from Uber make $1000 a month. So if a fulltime driverless (autonomous) car were to make that same amount it'd be making $52,000 a year. So if the car cost $100,000, in the the first two years the car would make no money but then from year 3 on it'd be making $50,000 profit (minus gas/maintenance/insurance). Btw autonomous cars do not cost $100,000. Estimates are that by 2025 driverless tech can be added to a car for $7,000 - $10,000 and may eventually go as low as $3,000 in much later years.
They will be able to decrease the cost because they don't have to pay drivers. Currently a full time driver is a reoccurring cost of $4000 a month for uber. Meaning from now to 5 years from now (or however long they work there) the driver would have cost uber $4000 (60) or $240,000 in 5 years. A driverless car would have a one time capital cost (the price of the car: it could be $10k, $20k, $50k, $100k, as long as it isn't some insanely large number which it isn't) and then after that cost is paid off instead of costing uber $4000 a month it'd be making them $4000 a month. So if it takes two years ($100,000 cost of the car) for the driverless/autonomus car to make back it's capital cost in year 3 it'd be making uber $4000 a month. In 5 years a driver would cost uber $240k and a driver less car would make then $150k. That's a $400,000 difference.