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 (
    86394, 86283, 86282, 86281, 86280, 86279, 
    86278, 86277, 86276, 86275, 85925, 
    85922, 85921, 85920, 85919, 85918, 
    85917, 85916, 85915, 85914
  ) 
  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 0.00066

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
85914 1.69000000
85915 1.69000000
85916 1.69000000
85917 1.69000000
85918 1.69000000
85919 1.69000000
85920 1.69000000
85921 1.69000000
85922 1.69000000
85925 1.69000000
86275 1.69000000
86276 1.69000000
86277 1.69000000
86278 1.69000000
86279 1.69000000
86280 1.69000000
86281 1.69000000
86282 1.69000000
86283 1.69000000
86394 1.69000000