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 (
    86725, 86724, 86723, 86561, 86560, 86558, 
    86557, 86556, 86555, 86554, 86553, 
    86552, 86551, 86825, 86824, 86823, 
    86822, 86821, 86820, 86819
  ) 
  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 0.00055

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
86551 1.69000000
86552 1.69000000
86553 1.69000000
86554 1.69000000
86555 1.69000000
86556 1.69000000
86557 1.69000000
86558 1.69000000
86560 1.69000000
86561 1.69000000
86723 1.69000000
86724 1.69000000
86725 1.69000000
86819 1.69000000
86820 1.69000000
86821 1.69000000
86822 1.69000000
86823 1.69000000
86824 1.69000000
86825 1.69000000