$fileList = Get-ChildItem C:\Lab
foreach ($item in $fileList){
    if ($item.length/1MB -lt 2){
        $item | Add-Member -MemberType NoteProperty -Name RarValue -Value "50000" -PassThru | Select FullName,RarValue
    }
    elseif ($item.length/1MB -lt 5){
        $item | Add-Member -MemberType NoteProperty -Name RarValue -Value "100000" -PassThru | Select FullName,RarValue
    }
    else {
        $item | Add-Member -MemberType NoteProperty -Name RarValue -Value "500000"-PassThru | Select FullName,RarValue
    }
}