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 (
    103770, 103769, 103768, 103767, 103766, 
    103765, 103764, 103763, 103762, 103761, 
    103760, 103759, 103758, 103757, 103756, 
    103755, 103754, 103753, 103752, 103751
  ) 
  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 0.00052

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
103751 1.69000000
103752 1.69000000
103753 1.69000000
103754 1.69000000
103755 1.69000000
103756 1.69000000
103757 1.69000000
103758 1.69000000
103759 1.69000000
103760 8.99000000
103761 1.69000000
103762 1.69000000
103763 1.69000000
103764 1.69000000
103765 1.69000000
103766 1.69000000
103767 1.69000000
103768 1.69000000
103769 1.69000000
103770 1.69000000