How can people afford a mortgage today?

I have am a recent graduate from graduate school and am looking to buy my first house, as I believe it is better than renting. Yet a small, yet decent place, to live is impossible to find for under $300K! Is buying a house even an option in today's society, or am I going to be stuck living in my parents house forever?
Added (1). Yes, I am well aware of what a mortgage is. 20% of $300K is still $60,000. My parents are poor. There is no way they will help me buy a house.
Added (2). I should also add that my boyfriend (who will be out of the military in 6 months) will also be living with me and contributing to the mortgage, but he still needs to secure another job.
Added (3). In my area, you cannot buy a mobile home for under $200,000. Its so bad.

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