$data = array(
    array(
        'modname' => 'Lorem',

        'pricing' => array(
            '0' => 0.03,
            '1' => 0.15,
            '2' => 0.50
        ),

        'names' => array(
            '0' => 'Lorems +0.03',
            '1' => 'Ipsum +0.15',
            '2' => 'Dolor +0.50'
        )

    ),

    array(
        'modname' => 'Ipsum',

        'pricing' => array(
            '0' => 0.08,
            '1' => 0.20,
            '2' => 0.60
        ),

        'names' => array(
            '0' => 'Sie +0.08',
            '1' => 'A +0.20',
            '2' => 'Mat +0.60'
        )

    )

);

$input = [
           ['id_group' => 1, 'name' => "Lorem", 'price' => 0.03],
           ['id_group' => 2, 'name' => "Sie",   'price' => 0.08],
           ['id_group' => 1, 'name' => "Ipsum", 'price' => 0.15],
           ['id_group' => 1, 'name' => "Dolor", 'price' => 0.50],
           ['id_group' => 2, 'name' => "A",     'price' => 0.20],
           ['id_group' => 2, 'name' => "Mat",   'price' => 0.60],
    ];

$result = [];
foreach($input as $d){
    $gId = $d['id_group'];

    //новая группа
    if(!isset($result[$gId])){
        $result[$gId] = [
                'modname' => $d['name'],
                'pricing' => [],
                'names'   => [],
             ];
    }

    $result[$gId]['pricing'][] = $d['price'];
    $result[$gId]['names'][] = sprintf("%s %+.2f", $d['name'], $d['price']);
}

Array (
[1] => Array
    (
        [modname] => Lorem
        [pricing] => Array
            (
                [0] => 0.03
                [1] => 0.15
                [2] => 0.5
            )

        [names] => Array
            (
                [0] => Lorem +0.03
                [1] => Ipsum +0.15
                [2] => Dolor +0.50
            )

    )

[2] => Array
    (
        [modname] => Sie
        [pricing] => Array
            (
                [0] => 0.08
                [1] => 0.2
                [2] => 0.6
            )

        [names] => Array
            (
                [0] => Sie +0.08
                [1] => A +0.20
                [2] => Mat +0.60
            )

    )