I see I missed something there.
Please replace the following line in soft79-wc-pricing-rules.php (line 178):
return sprintf( _x( '%1$s–%2$s', 'Price range: from-to', 'woocommerce' ), wc_price( $min_price ), wc_price( $max_price ) );
with
return sprintf( _x( '%1$s–%2$s', 'Price range: from-to', 'woocommerce' ), wc_price( $product->get_display_price( $min_price ) ), wc_price( $product->get_display_price( $max_price ) ) );
Please let me know if this fixes the issue for you.
I will release a fix within a couple of days.