DOWNTOWN LOS ANGELES (KABC) -- It's already expensive to live in Southern California, but rents are expected to keep going up over the next two years, according to a new University of Southern California forecast.The Casden Real Estate Forecast predicts apartment construction increasing for the next two years, but not enough to meet demand.The result is likely to be an average rent increase of around $109 per month in Los Angeles County, $149 for Orange County and $84 in the Inland Empire.Brokers and builders say California is the most difficult place in the country to build new housing because of government red tape and neighborhood opposition to gentrification.The only hope for middle-class renters, some experts suggest, is when traditional high-income renters decide to move to single-family homes. That would then leave a greater focus on the market for renters of more modest means.