How to count ACF Flexible Content Rows?

If your count is purely just to add a number on the end of your count- class then you can achieve this by using a variable just outside the loop and adding to the variable at the end.

<?php if( have_rows('pricing_tables') ): ?>

<div class="columns">
    <?php $count = 0; ?>
    <?php while ( have_rows('pricing_tables') ) : the_row(); ?>

        <?php if( get_row_layout() == 'price_table' ): ?>

            <?php $count = count(get_sub_field('price_table')); ?>

            <div class="one-half first count-<?php echo $count; ?> index-<?php echo get_row_index(); ?>">

                <?php the_sub_field('title'); ?>

            </div>
            <?php $count++; ?>
        <?php endif; ?>

    <?php endwhile; ?>

</div>

You keep getting the value 1 because each time the loop got to your module layout price_table you were counting the layout.

If you wanted to count the total number of layouts used within your flexible content area for your page then you should count the field which is your flexible content area and not the individual layout

$count = count(get_field('pricing_tables'));

I hope that helps