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 (
    103719, 103718, 103806, 103805, 103804, 
    103803, 103802, 103801, 103800, 103799, 
    103798, 103797, 103796, 103795, 103794, 
    103793, 103792, 103773, 103772, 103771
  ) 
  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 0.00074

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
103718 1.69000000
103719 1.69000000
103771 1.69000000
103772 1.69000000
103773 8.99000000
103792 1.69000000
103793 1.69000000
103794 1.69000000
103795 1.69000000
103796 1.69000000
103797 1.69000000
103798 1.69000000
103799 1.69000000
103800 1.69000000
103801 1.69000000
103802 1.69000000
103803 1.69000000
103804 1.69000000
103805 1.69000000
103806 8.99000000