How to sort by number

by

You are using pre 4.5.0 code which will eventually be depricated. Try this.

$productTerms = get_terms( array(
    'taxonomy' => 'prezzoceste',
    'hide_empty' => false,
    'orderby' => 'ASC',
    'meta_key' => '_price', //The price Meta Key
    'orderby' => 'meta_value_num',
) );

Check this for more accepted arguments.