There are big value differences between the models, early Metrallas are worth a lot, at least here in Europe and getting rare too, you don't find them everyday and everywhere.
Your Metralla modell 8 should be a "Metralla 62", build 1962 - 1966. Number start from 800.001 to 804.919.
The model you can buy should have a number somwhere in between.
This is the very first Metralla model!