public class Item
{
  public Long id;
}

public class Contract
{
  public Long id;
  public Collection<ContractItem> items;
}

public class ContractItem
{
  public Long id;
  public Contract contract;
  public Item item;
  public BigDecimal price;
}

SELECT i.id, ci1.price, ci2.price, ...
FROM Items i
  LEFT JOIN ContractItem ci1 ON ci1.item = i.id
  LEFT JOIN ContractItem ci2 ON ci2.item = i.id
  ...
WHERE ci1.contract = ? AND ci2.contract = ? AND ...