Florida. Having trouble compiling information about the process of my fiancée moving to the USA from Australia?

After looking at the incredibly high costs of living in Sydney and the disproportionately high cost of obtaining a partner visa in Australia, it's looking like America might be the best country for the gap to be closed in my long-distance relationship. This is my best understanding of the process:

1. She'd apply for a K-1 Fiancee visa. According to a bit of googling, this costs about $350-$1000 USD, and requires us to have met within the past two years in person (which we've done). This would allow her to stay here for ninety days and we could get married during that time.

2. After that.... I honestly have no idea, it seems like there's a lot more bureaucracy involved in the process from going from AUS->USA over USA->AUS, or the USA's immigration site is just harder for me to understand than AUS'.

I suppose I just have a few basic questions to ask about that for now for the sake of guidance, although any additional information would be greatly appreciated, because I'm really lost. She'd want to become a citizen of the US, and Australia allows its citizens to hold dual citizenship.

1. After we get married, does she have to leave the country after that 90 day period while whatever visa she needs to remain is taken care of?

2. How soon would she be able to work or attend university after marriage?

3. About how much would this process be expected to cost?