$tabs = 'tabs' . ( "\t" x $numTabs );
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You have the canonical answer from jwkrahn. However your code indicates a few opportunities for learning.

First off always use strictures (use strict; use warnings;).

Perl programers seldom use a C style for. The more usual way to iterate a fixed number of times is:

for my $index (1 .. $numTabs) {
   ...
}
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Although in the case in hand you don't need the counter at all. You could just:

for (1 .. $numTabs) {
   ...
}
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and if there is only one simple statement in the loop you can use the for as a modifier:

... for 1 .. $numTabs;
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I suspect there is a transcription error in your sample code. Most likely what you intended was:

$tabs = "$tabs\t";
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in which case Perl allows you to use the concatenation assignment operator:

$tabs .= "\t";
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so a more Perlish technique (without using the x operator) is

$tabs .= "\t" for 1 .. $numTabs;
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Cool. Thanks a lot.

for ($i = 0; $i < $numTabs; $i++) {
  $tabs .= "\t";
}
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But, like jwkrahn wrote: you might as well use x instead of the loop, so this becomes:

$tabs .= "\t" x $numTabs;
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Thank you.