I like Randal's answer even if it is technically wrong as you 
need $1023 to make it work! Some really interesting syntax there.
Naturally you want a geometric progression. 
This is short, but very un-obfu ;-)

tachyon

print "Enter an integer 1-1000 :";
my $amount = <>;
#die "Integers 1-1000 only!\n" unless $amount =~ m/^\d{1,4}$/ and $amo
+unt <= 1000 and $amount > 0;
my @envelope = qw(1 2 4 8 16 32 64 128 256 490);
for (reverse @envelope) {
    next if $_ > $amount;
    printf "Giving you envelope with \$%d.00\n", $_;
    $amount -= $_;
}
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