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 (
    86768, 86767, 86766, 86765, 86764, 86763, 
    86762, 86761, 86760, 86593, 86576, 
    86573, 86571, 86569, 86567, 86565, 
    86547, 86448, 86416, 86773
  ) 
  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 0.00050

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
86416 1.69000000
86448 1.69000000
86547 1.69000000
86565 1.69000000
86567 1.69000000
86569 1.69000000
86571 1.69000000
86573 1.69000000
86576 1.69000000
86593 1.69000000
86760 1.69000000
86761 1.69000000
86762 1.69000000
86763 1.69000000
86764 1.69000000
86765 1.69000000
86766 1.69000000
86767 1.69000000
86768 1.69000000
86773 1.69000000