The government can subsidize the costs and offer service for well below the actual costs, which is unfair competition.
The issue in high costs with broadband come from partial or complete monopolies of ISPs. ISPs like Comcast can charge whatever they want in many areas because they are the only viable option.
In order to reduce costs, the government can help introduce competition. When many companies offer similar service, they compete for customers in price and customers win. I really like this idea in Virginia of providing a means for municipalities to introduce competition rather than become competitors themselves. It provides a means to offer lots of competition to companies like Comcast. This is something Comcast fights with a passion since they won't make as much money.