Got it working in the end with the below code:
<?php
$args = array(
'posts_per_page'=> -1,
'post_type' => 'properties',
'meta_key' => 'development',
'meta_value' => $development_id,
);
$properties_query = new WP_Query( $args );
$prices = array();
if( $properties_query->have_posts() ):
while( $properties_query->have_posts() ) : $properties_query->the_post();
$price = get_field('price');
if(isset($price) && !empty($price)){
$prices[] = $price;
}
endwhile;
$max_price = max($prices);
$min_price = min($prices);
endif; wp_reset_query();
?>