根据你的问题，我认为这是最简单的查询，你可以运行得到你想要的结果。

insert into service_plan (service_id, plan_id, price) select s.id, p.id, 200 from services as s cross join plans as p

为什么要抵制交叉联接？

drop table if exists PLANS,SERVICES,SERVICE_PLAN;

create table plans
(id int,name varchar(100),  description varchar(100));
insert into plans values
(1, 'plan one'  ,'description for plan one'),
(2, 'plan two'  ,'description for plan two');

create table services
(id int, name varchar(20));
insert into services values
(1  ,'service one'),
(2  ,'services two');

create table service_plan
(id int auto_increment primary key, service_id int, plan_id int, price int not null default 200);

insert into service_plan(service_id,plan_id) 
select s.id,p.id
        from plans p
cross join services s
order by s.id,p.id;

select * from service_plan;

+----+------------+---------+-------+
| id | service_id | plan_id | price |
+----+------------+---------+-------+
|  1 |          1 |       1 |   200 |
|  2 |          1 |       2 |   200 |
|  3 |          2 |       1 |   200 |
|  4 |          2 |       2 |   200 |
+----+------------+---------+-------+
4 rows in set (0.001 sec)