The cost of settling China's rural workers into city life in the government's urbanization drive could be about 650 billion yuan ($106 billion) a year, the equivalent of 5.5 percent of fiscal revenue last year, a government think-tank said on Tuesday.

The figure is based on the assumption that 25 million people a year settle in cities, with the government spending the money on making sure they enjoy the same benefits in healthcare, housing and schools that city residents have, the Chinese Academy of Social Sciences (CASS) said.

"I think the biggest obstacle for turning rural migrant workers into urban citizens is the cost issue," Wei Houkai, a researcher at CASS, told a news conference, adding that to achieve equality of treatment could take until 2025.

Millions of migrant workers from the countryside and smaller towns work in China's big cities, often in low-paid manual work, but lack access to education, health and other services tied to the country's strict household registration - or hukou - system.

China sees the urbanization drive as pushing domestic consumption, which it wants to make the main engine of growth for the economy, replacing exports and manufacturing and investment.

Rural migrant laborers only earned an average 2,049 yuan a month in 2011, or 59 percent of average urban workers' salary, CASS added.

But they need to pay about 18,000 yuan annually per capita to be able to live in cities and another 100,000 yuan on average for housing, it said.