Create 2 tables
Item(id) and Item_log(item_id, price)

Populate it
insert into item(id) values(1);
insert into item(id) values(2);
insert into item(id) values(3);
insert into item(id) values(4);

insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(2, 200);
insert into item_log(item_id, price) values(2, 200);

Run SQL
SELECT COUNT(il.price), i.id AS item_id, il.price
FROM item i, item_log il
WHERE i.id = il.item_id GROUP BY il.price, i.id;

Result
count | item_id | price
——-+———+——-
3 | 1 | 100
6 | 1 | 200
2 | 2 | 200

Run SQL
SELECT COUNT(il.price), i.id AS item_id, il.price, array_accum(il.id) AS item_id_array
FROM item i, item_log il
WHERE i.id = il.item_id
GROUP BY il.price, i.id;

Result
count | item_id | price | item_id_array
——-+———+——-+—————
3 | 1 | 100 | {1,2,3}
6 | 1 | 200 | {4,5,6,7,8,9}
2 | 2 | 200 | {10,11}