in some area of U.S, such as New York and San Francisco, 100k is not too much because the living cost is too high. If your friend is a single, he/she needs to give U.S about one third for tax.
The working-class households in San Francisco Bay Area earn over $50,000 a year (e.g., in service sectors). The median household income of San Francisco is about $80,000 a year. If one makes only $100,000 a year, it would be hard to buy a house in San Francisco. A family of four is qualified for housing assistance in San Francisco if the household income is $90,500 (HUD Low Income Category).