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 (
    104706, 104705, 104704, 104703, 104914, 
    102266, 102265, 104696, 104697, 104538, 
    104537, 104536, 104535, 104534, 104533, 
    104532, 104531, 104526, 104525, 104524
  ) 
  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 0.00072

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
102265 1.69000000
102266 1.69000000
104524 1.69000000
104525 1.69000000
104526 1.69000000
104531 1.69000000
104532 1.69000000
104533 1.69000000
104534 1.69000000
104535 1.69000000
104536 1.69000000
104537 1.69000000
104538 1.69000000
104696 1.69000000
104697 1.69000000
104703 1.69000000
104704 1.69000000
104705 1.69000000
104706 1.69000000
104914 1.69000000