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 (
    104382, 104381, 104380, 104379, 102165, 
    102164, 102163, 102162, 102161, 102160, 
    102159, 102158, 102157, 102156, 102155, 
    102154, 102150, 104598, 102142, 102141
  ) 
  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 0.00065

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
102141 1.69000000
102142 1.69000000
102150 1.69000000
102154 1.69000000
102155 1.69000000
102156 1.69000000
102157 1.69000000
102158 1.69000000
102159 1.69000000
102160 1.69000000
102161 1.69000000
102162 1.69000000
102163 1.69000000
102164 1.69000000
102165 1.69000000
104379 1.69000000
104380 1.69000000
104381 1.69000000
104382 1.69000000
104598 1.69000000