public class Cost
{
    public decimal PurchasePrice { get;  }
    public decimal EstimatedRetailPrice { get;  }
    public decimal SalesPrice { get;  }

    public Cost() {}

    public Cost(decimal purchasePrice = 0, decimal estimatedRetailPrice = 0, decimal salesPrice = 0)
    {
        PurchasePrice = purchasePrice;
        EstimatedRetailPrice = estimatedRetailPrice;
        SalesPrice = salesPrice;
    }
}

public static class EntityTypeBuilderExtensions
{
    /// <summary>
    /// Allows an immutable object to be defined as an 'Owned Entity Type' in EF .
    /// </summary>
    /// <typeparam name="TEntity"></typeparam>
    /// <typeparam name="TRelatedEntity"></typeparam>
    /// <param name="entityTypeBuilder"></param>
    /// <param name="expression"></param>
    public static void OwnsOneImmutable<TEntity, TRelatedEntity>(this EntityTypeBuilder<TEntity> entityTypeBuilder, Expression<Func<TEntity, TRelatedEntity>> expression)
        where TEntity : class
        where TRelatedEntity : class
    {
        var constructor = typeof(TRelatedEntity).GetConstructor(Type.EmptyTypes);
        if (constructor == null)
            throw new InvalidOperationException($"Class '{typeof(TRelatedEntity).Name}' does not contain a parameterless constructor.");

        var builder = entityTypeBuilder.OwnsOne(expression);

        var fieldInfos = typeof(TRelatedEntity).GetFields(BindingFlags.NonPublic | BindingFlags.Instance).ToList();
        var propertyInfos = typeof(TRelatedEntity).GetProperties(BindingFlags.GetProperty | BindingFlags.Instance | BindingFlags.Public);

        foreach (var propertyInfo in propertyInfos)
        {
            var fieldInfo = fieldInfos.Single(x => x.Name == $"<{propertyInfo.Name}>k__BackingField");
            builder.Property(propertyInfo.PropertyType, propertyInfo.Name).HasField(fieldInfo.Name);
        }
    }
}