SQL & PL/SQL :: Select In Case Statement

I have the following tables:

create table lookups (code varchar2(20), amount number);

insert into lookups values ('Rent' , 500);
insert into lookups values ('Breakpoint' , 10);

create table products (id number, cost number, year varchar2(4));

insert into products values (1, 1000, '2011');
insert into products values (1, 2000, '2011');
insert into products values (2, 100, '2011');
insert into products values (3, 50, '2011');

commit;

I want to write a query which lists the IDs and the sum(cost), and a Y/N indicator which is set to 'Y' IF sum(cost) > ( (lookups.rent value) * (100 - lookups.breakpoint value))/100

I have written this query:

SELECT id,
sum(cost)cost,
year,
CASE
WHEN cost >
((SELECT amount
[code]....... ORDER BY id;

This returns

ID COST YEAR YN
--------- ---------- ---- -
1 1000 2011 Y
1 2000 2011 Y
2 100 2011 N
3 50 2011 N

The YN is correct, but it needs to sum the amounts. So there should only be one row for id1 = 3000.e.g.

ID COST YEAR YN
--------- ---------- ---- -
1 3000 2011 Y
2 100 2011 N
3 50 2011 N

I am not sure how to do this. Or is there a better way of doing this than using CASE.