Only display price when value exist

Question

Assuming this produces the first price currently:

echo '<th>' . wpforest_currency_simb() . get_post_meta( $post_id->ID, 'WpForest_price', true ) . ' ' . get_option( 'wpf_paypal_cur' ) . '</th>';z

And assuming I understand the question, this should test for the first price:

$price = get_post_meta( $post_id->ID, 'WpForest_price', true );
if ( $price )
    echo '<th>' . wpforest_currency_simb() . "$price " . get_option( 'wpf_paypal_cur' ) . '</th>';

And this should test for the second price:

$price = get_post_meta( $post_id->ID, 'WpForest_price 1', true );
if ( $price )
    echo '<th>' . wpforest_currency_simb() . "$price " . get_option( 'wpf_paypal_cur' ) . '</th>';

From the comments it appears you want this:

if ( some test )
    $price = get_post_meta( $post_id->ID, 'WpForest_price', true );
else
    $price = get_post_meta( $post_id->ID, 'WpForest_price 1', true );

echo '<th>' . wpforest_currency_simb() . "$price " . get_option( 'wpf_paypal_cur' ) . '</th>';

But I cannot tell what test you want to use.