Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE products ( product_id VARCHAR, product_price VARCHAR )
TABLE: CREATE TABLE staff ( last_name VARCHAR, staff_id VARCHAR )
TABLE: CREATE TABLE complaints ( staff_id VARCHAR, product_id VARCHAR )

### Question ###
Find the last name of the staff member who processed the complaint of the cheapest product.

### Accurate SQL ###

SELECT t1.last_name FROM staff AS t1 JOIN complaints AS t2 ON t1.staff_id = t2.staff_id JOIN products AS t3 ON t2.product_id = t3.product_id ORDER BY t3.product_price LIMIT 1