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 (
    106238, 106237, 106236, 106235, 106234, 
    106233, 106680, 106285, 106284, 106556, 
    106371, 106370, 106208, 106232, 106179, 
    106178, 106177, 106176, 106175, 106174
  ) 
  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 0.00059

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
106174 1.69000000
106175 1.69000000
106176 1.69000000
106177 1.69000000
106178 1.69000000
106179 1.69000000
106208 1.69000000
106232 1.69000000
106233 1.69000000
106234 1.69000000
106235 1.69000000
106236 1.69000000
106237 1.69000000
106238 1.69000000
106284 1.69000000
106285 1.69000000
106370 1.69000000
106371 1.69000000
106556 1.69000000
106680 1.69000000