Names with modifiers are an indicator that you should be using a hash instead of separate variables. Instead of $price_high, it might be an idea to use $price{high}.

How about something like ...

open STOCKS, ">",  $dataFileName or die $!;
my $price;
PRICES:
for my $category ( qw( high low average purple green ) ) {
    for my year ( 1990..2000 ) {
        last PRICES unless $price = <STOCKS>; # break loop at eof.
        $prices{$category}{$year} = $price;
    }
}
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