Maybe instead of a parallel array or arrayreferences, just use a single array with the even offsets being the threshholds and the odd offsets being the clamped values?

use strict;
use vars qw(@lookup_values);
@lookup_values= (qw(
           25000       2500
           50000       5000
          150000      12500
          225000      25000
          300000      37500
          600000      60000
         1200000     120000
         3600000     300000
         5400000     600000
        10800000     900000
        21600000    1800000
        43200000    3600000
        64800000    7200000
       129600000   10800000
       216000000   21600000
       432000000   43200000
       864000000   86400000
      1728000000  172800000
      3024000000  345600000
      6048000000  604800000
     12096000000 1209600000
     31557600000  2629800000
     63115200000  5259600000
     78894000000  7889400000
    157788000000 15778800000
                 
));

sub lookup {
    my $v= $_[0];
    return 31557600000 if $v >= 157788000000;
    my $i;
    for( $i= 0; $i <= $#lookup_values-1 && $v >= $lookup_values[$i]; $
+i+=2 ) {
        # nothing in the loop body
        #print "$v: $i -> $lookup_values[$i]\n";
    };
    return $lookup_values[ $i+1 ];
};


for( 10,2500,2501, 157788000000, 157788000001, 78894000000 ) {
    print sprintf "%d => %d\n", $_, lookup($_);
};
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