SELECT 
  cscart_product_prices.product_id, 
  MIN(
    IF(
      cscart_product_prices.percentage_discount = 0, 
      cscart_product_prices.price, 
      cscart_product_prices.price - (
        cscart_product_prices.price * cscart_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  cscart_product_prices 
WHERE 
  cscart_product_prices.product_id IN (
    93938, 92908, 92679, 93934, 93931, 93930, 
    93929, 93927, 93907, 93906, 93905, 
    93902, 93796, 93784, 93544, 93459, 
    93069, 93068, 93797, 93774
  ) 
  AND cscart_product_prices.lower_limit = 1 
  AND cscart_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  cscart_product_prices.product_id

Query time 0.00067

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_product_prices range usergroup,product_id,lower_limit,usergroup_id usergroup 9 40 Using where

Result

product_id price
92679 1.69000000
92908 1.69000000
93068 1.69000000
93069 1.69000000
93459 1.69000000
93544 1.69000000
93774 1.69000000
93784 1.69000000
93796 1.69000000
93797 1.69000000
93902 1.69000000
93905 1.69000000
93906 1.69000000
93907 1.69000000
93927 1.69000000
93929 1.69000000
93930 1.69000000
93931 1.69000000
93934 1.69000000
93938 1.69000000