Your forecastStr is not the property name. It is "coll.{propertyname}".
The problem is that your line:
PropertyInfo pinfo = typeof(NCAABArchive).GetProperty(forecastStr);
is not getting a property because there's not a property called "coll.Linefox".
So pinfo is null and returning the error when you try to access it.
string propName = "LineAvg"
PropertyInfo pinfo = typeof(NCAABArchive).GetProperty(propName);
object value = pinfo.GetValue(coll)
// "value" will be set to coll.LineAvg