Virginia is facing a huge bill for unexpected Medicaid costs that hamper proposed new spending on things like school improvements or tax breaks for the poor. State officials said Friday that Virginia has about $460 million in unforeseen Medicaid costs. Secretary of Finance Aubrey Layne said much of the new costs stem from faulty forecasts overestimating the benefits of having private health insurers cover a greater number of some of the state’s more costly Medicaid recipients. Another reason for the increase is a higher-than-expected enrollment of children in the state’s Medicaid program, he said.