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 (
    106331, 106330, 106329, 106328, 106327, 
    106326, 106325, 106324, 106323, 106312, 
    106311, 106309, 106308, 106307, 106306, 
    106305, 106304, 106303, 106302, 106301
  ) 
  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 0.00063

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
106301 1.69000000
106302 1.69000000
106303 1.69000000
106304 1.69000000
106305 1.69000000
106306 1.69000000
106307 1.69000000
106308 1.69000000
106309 1.69000000
106311 1.69000000
106312 1.69000000
106323 1.69000000
106324 1.69000000
106325 1.69000000
106326 1.69000000
106327 1.69000000
106328 1.69000000
106329 1.69000000
106330 1.69000000
106331 1.69000000