如果我理解正确，你可以选择 part.price 在子查询和计算中 part.price * consists_of.quantitiy .
插入前

CREATE TABLE part(part_id INTEGER, price INTEGER);
CREATE TABLE consists_of(customer_id INTEGER, part_id INTEGER, quantity INTEGER, price INTEGER);

INSERT INTO part VALUES(10, 50);
INSERT INTO part VALUES (20, 1000);

CREATE TRIGGER IF NOT EXISTS raise_if_consists_of_price_too_expensive
AFTER INSERT ON consists_of
WHEN new.price > (SELECT part.price * new.quantity FROM part WHERE part.part_id = new.part_id)
BEGIN
  SELECT RAISE (ABORT, 'too expensive.');
END;

 -- OK
INSERT INTO consists_of(customer_id, part_id, quantity, price)
VALUES(10050, 20, 31, 100);
 -- OK
INSERT INTO consists_of(customer_id, part_id, quantity, price)
VALUES(80030, 10, 9, 50 * 9);
 -- Raise abort
INSERT INTO consists_of(customer_id, part_id, quantity, price)
VALUES(80099, 10, 9, 50 * 9 + 1);

插入后

CREATE TABLE part(part_id INTEGER, price INTEGER);
CREATE TABLE consists_of(customer_id INTEGER, part_id INTEGER, quantity INTEGER, price INTEGER);

INSERT INTO part VALUES(10, 50);
INSERT INTO part VALUES (20, 1000);

CREATE TRIGGER IF NOT EXISTS fill_consists_of_price
AFTER INSERT ON consists_of
BEGIN
  UPDATE consists_of
  SET
  price = (
    SELECT consists_of.quantity * part.price
    FROM part
    WHERE part.part_id = consists_of.part_id
  )
  WHERE customer_id = new.customer_id AND part_id = new.part_id
  ;
END;

INSERT INTO consists_of(customer_id, part_id ,quantity)
VALUES(10050, 20, 31);

INSERT INTO consists_of(customer_id, part_id ,quantity)
VALUES(80033, 10, 9);