import re
text = "5 000, 6 123 456,345 and 6 123 456.345... I mean 20 000 or 5 000 000. For example: 20 30"
print( re.findall(r'(?<!\d)(?<!\d[.,])\d{1,3}(?:\s\d{3})*(?:[,.]\d+)?', text) )
aW1wb3J0IHJlCnRleHQgPSAiNSAwMDAsIDYgMTIzIDQ1NiwzNDUgYW5kIDYgMTIzIDQ1Ni4zNDUuLi4gSSBtZWFuIDIwIDAwMCBvciA1IDAwMCAwMDAuIEZvciBleGFtcGxlOiAyMCAgICAzMCIKcHJpbnQoIHJlLmZpbmRhbGwocicoPzwhXGQpKD88IVxkWy4sXSlcZHsxLDN9KD86XHNcZHszfSkqKD86WywuXVxkKyk/JywgdGV4dCkgKQ==