i have added for price insert into orders values (430 k street',books,225); when (price > 150); dbms_output.put_line('too expensive '); END; i want to do is ,when price is over 150 ,will show too...

i have added for price <>
  ADD CONSTRAINT cost_price_ck CHECK (price <>
DECLARE
 price
BEGIN

    insert into orders  values (430 k street',books,225);
              when  (price > 150);
dbms_output.put_line('too expensive ');

END;

 i want to do is ,when price is over 150 ,will show too expensive
but i run this code, it show like this
PLS-00103: Encountered the symbol "BEGIN" when expecting one of the following:
   constant exception

table long double ref
   char time timestamp interval date binary national character
   nchar
06550. 00000 -  "line %s, column %s:\n%s"
*Cause:    Usually a PL/SQL compilation error.

whats the wrong with my code and how can I fix it ?