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 (
    8312, 10699, 8352, 9463, 8313, 10071, 
    8314, 414, 10073, 8373, 10072, 1628
  ) 
  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 0.00043

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 product_id 3 13 Using index condition; Using where

Result

product_id price
414 52.200000
1628 35.700000
8312 62.440000
8313 20.310000
8314 40.200000
8352 21.000000
8373 32.000000
9463 27.600000
10071 63.030000
10072 81.730000
10073 32.000000
10699 62.440000