The line $mins = "$mins.00"; turns the Math::BigInt object into a standard Perl scalar. If you inspect $mins using Data::Dumper before and after $mins = "$mins.00"; you get:

$VAR1 = bless( {
                 'value' => [
                              43200
                            ],
                 'sign' => '+'
               }, 'Math::BigInt' );

$VAR1 = '43200.00';
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So (with hindsight!) had you used Data::Dumper as a first step to see what's going on, you would have been told immediately. But this is only with hindsight...

Perhaps this time it is "Hindsight", but next time it could be "Lesson Learned", "Experience", "Defensive Programming", or, Monastary forbid, a "Good Engineering Practice".

This incident has added a rather large stone on the scale which was already precariously close to tipping in favor of switching to the use of Data::Dumper over my rather obsolete and unrobust homespun debug module from longer ago than I'd care to admit.

Thanks for the analysis and summary. Thanks to the OP for posting -- and clarifying -- the problem.

Yes, with hindsight! Funny how often we get the answer and then realize that the right 1st step would have solved it. Thank you!