Funny - I just wrote about this in another post. Partially quoting myself, the SQL for a multi-value insert like what you are doing is
INSERT INTO xyz (col1, col2)
VALUES ('a','b'),('c','d');
The query you are writing is not this form you have something like INSERT INTO xyz (object).
What you are likely looking to do is
INSERT INTO today_prices (cost_time, price_stock)
/* put your query4 SELECT statement here */