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 (
    97918, 97916, 97215, 97911, 97900, 97899, 
    97896, 97757, 97670, 97165, 97164, 
    97106, 92927, 96739, 97748, 97747, 
    97746, 92926, 97705, 97704
  ) 
  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 0.00125

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
92926 1.69000000
92927 1.69000000
96739 1.69000000
97106 1.69000000
97164 1.69000000
97165 1.69000000
97215 1.69000000
97670 1.69000000
97704 1.69000000
97705 1.69000000
97746 1.69000000
97747 1.69000000
97748 1.69000000
97757 1.69000000
97896 1.69000000
97899 1.69000000
97900 1.69000000
97911 1.69000000
97916 1.69000000
97918 1.69000000