SELECT 
  cscart_ult_product_prices.product_id, 
  MIN(
    IF(
      cscart_ult_product_prices.percentage_discount = 0, 
      cscart_ult_product_prices.price, 
      cscart_ult_product_prices.price - (
        cscart_ult_product_prices.price * cscart_ult_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  cscart_ult_product_prices 
WHERE 
  cscart_ult_product_prices.product_id IN (
    8306, 8289, 8361, 8304, 9885, 8367, 9882, 
    8288, 8275, 8733, 8362, 8305
  ) 
  AND cscart_ult_product_prices.lower_limit = 1 
  AND cscart_ult_product_prices.company_id = 1 
  AND cscart_ult_product_prices.usergroup_id IN (0, 0, 1) 
GROUP BY 
  cscart_ult_product_prices.product_id

Query time 0.00052

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_ult_product_prices range usergroup,product_id,company_id,lower_limit,usergroup_id usergroup 13 24 Using index condition

Result

product_id price
8275 85.140000
8288 61.960000
8289 61.960000
8304 53.420000
8305 70.480000
8306 70.480000
8361 88.400000
8362 82.070000
8367 34.560000
8733 126.000000
9882 63.750000
9885 39.860000