I'm using a different bcrypt module, Crypt::Eksblowfish::Bcrypt, and am observing that instead of a hex digest, it stores both the settings and the salt in the output hash:

length = 11
  $2a$11$WUHhXETkX0fnYkrqZU3ta.SjqJkrtBHwUGTHlTfGO1BINxczZnBJm
length = 12
  $2a$12$WUHhXETkX0fnYkrqZU3ta.D8cEIQdqzSrGG5wFTandtdP9Ypqzu0W
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Therefore, your JSON-like storage should not be needed. This is the code I was using:

use Time::HiRes 'time';
use Crypt::Eksblowfish::Bcrypt qw(bcrypt en_base64);

sub _salt() {
        return en_base64('abcdefghijklmnop');
}

my $cost = sprintf("%02d", $ARGV[0]);
my $settings = join( '$', '$2a', $cost, _salt() );

my $st = time();
print bcrypt("password", $settings), "\n";
printf "took %i milliseconds\n", (time() - $st) * 1000;
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I suspect a cost of 11-14 is good enough to deter brute force and even some dictionary attacks on today's hardware, while not bogging down your server -- depending of course on the security requirements and the amount and frequency of users needing to log in.