Get single product price in Submission Data

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1

I am using this snippet for setup the fee for recurring payments. Anybody tell me how i can get the single product price in this snippet. I want to minus that price from total recurring payment. I have used this rgar( $entry, ‘66’ ); but its showing null value.
@chrishajer

//Setup fee for registration programs
add_filter( 'gform_submission_data_pre_process_payment_121', 'modify_submission_data_121', 10, 4 );
function modify_submission_data_121( $submission_data, $feed, $form, $entry ) {
    //Setup depsit fee for first recurring payment
    $submission_data['setup_fee'] = rgar( $entry, '66' );
    GFCommon::log_debug( __METHOD__ . '(): Setup fee for trial form: ' . $submission_data['setup_fee'] );
    //Minus setup depsit fee from total price
    $submission_data['payment_amount'] = rgar( $entry, '35' ) - rgar( $entry, '66' );
    GFCommon::log_debug( __METHOD__ . '(): Setup fee for trial form: ' . $submission_data['payment_amount'] );
    return $submission_data;
}
2

@chrishajer Could you please respond to this issue?

I want to remove the setup fee from form total but this snippet not working

$submission_data['payment_amount'] = rgar( $entry, '35' ) - rgar( $entry, '66.2' );