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 (
    95318, 95317, 95316, 95315, 95314, 95313, 
    95312, 95311, 95310, 95309, 95308, 
    95307, 98602, 94670, 94299, 94252, 
    94163, 94162, 94161, 94160
  ) 
  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 0.00107

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
94160 1.69000000
94161 1.69000000
94162 1.69000000
94163 1.69000000
94252 1.69000000
94299 1.69000000
94670 1.69000000
95307 1.69000000
95308 1.69000000
95309 1.69000000
95310 1.69000000
95311 1.69000000
95312 1.69000000
95313 1.69000000
95314 1.69000000
95315 1.69000000
95316 1.69000000
95317 1.69000000
95318 1.69000000
98602 1.69000000