DecimalModelBinder.cs

public class DecimalModelBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var valueResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        var modelState = new ModelState { Value = valueResult };

        object actualValue = null;

        if (string.IsNullOrEmpty(valueResult.AttemptedValue))
        {
            actualValue = bindingContext.ModelType.IsValueType 
                ? Activator.CreateInstance(bindingContext.ModelType) : null;
        }
        else
        {
            try
            {
                actualValue = Convert.ToDecimal(valueResult.AttemptedValue, CultureInfo.GetCultureInfo("nb-NO"));
            }
            catch (FormatException e)
            {
                modelState.Errors.Add(e);
            }
        }

        bindingContext.ModelState.Add(bindingContext.ModelName, modelState);
        return actualValue;
    }
}