Like this, you mean? What you are trying to do is not completely clear to me from your description.

#!/usr/bin/perl -w

use strict;

# create some dummy data
my %in;
$in{"COST_1"} = 20;
$in{"COST_2"} = 30;
$in{"REPORTID_1"} = 3232;
$in{"REPORTID_2"} = 3483;
$in{"records"} = 2;

my $linecounter = 1;
my $records = $in{'records'};
open(FILE, ">outfile") or die "outfile: $!";
while ($linecounter <= $records) {
   my $thiscost = $in{"COST_$linecounter"} * 100;
   print FILE $in{"REPORTID_$linecounter"}, " ";
   print FILE $thiscost, "\n";
   $linecounter++;
}
close FILE;
[download]

>cat outfile
3232 2000
3483 3000