query: last N price for each product?

Dear SQL masters,

The query for "latest price for each product" goes like this (which I
can grasp quite easily):

 SELECT * FROM price p1
 WHERE ctime=(SELECT MAX(ctime) FROM price p2 WHERE
p1.product_id=p2.product_id)

or:

 SELECT * FROM price p1
 WHERE NOT EXISTS (SELECT * FROM price p2 WHERE
p1.product_id=p2.product_id AND p1.ctime < p2.ctime)

but how do yo query for "latest 3 prices for each product"? The
"price" table contains current price as well as price histories.

Regards,
dave

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