If I live in St. Louis MO and I move to San Diego CA, roughly how much would it cost me to drive there, and for 1 flight from st. louis to san diego?

Sites like aaa.com have gas calculators so you can put in your type of car and from where to where and it'll tell you the approximate gas cost. And travel sites like hotwire or orbit can give you flight price information.

Yeah triple A is good with all those ?'s
It is approximately 1,853 mi – about 1 day 2 hours
Divided by 20 miles ? To a gallon @ $4.00 per gallon I would estimate approx $350.00 to $00. But you should get better gas mileage on the highway.
Plane tickets vary a lot depending on when you want to go and stand by and all.

Also check with how much the cost of living is.
I always heard that to rent they charge you security, first and last month rent and utility turn on and it costs around $2,000. Just to move in