function get_price(pv_price_proc in varchar2, pn_prod_id in number, pd_date in date) return number is  
  lv_stmt varchar2(255);
  lv_price number;
begin
  lv_price := null;

  lv_stmt := 'BEGIN :lv_price := '||pv_price_proc||'('||pn_prod_id||', '||to_char(pd_date,'DD.MM.YYYY')||'); END;';
  EXECUTE IMMEDIATE lv_stmt USING IN OUT lv_price;

  return lv_price;
end;

select 
        o.order_id,
        get_price(o.price_proc, o.prod_id, o.order_date) as price
from 
        orders o
where 
    o.order_date = sysdate 

lv_stmt := 'select :pv_price_proc (:pn_prod_id, :pd_date) from dual';
EXECUTE IMMEDIATE lv_stmt into lv_price USING pv_price_proc, pn_prod_id, pd_date;