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 (
    111706, 111705, 111704, 111703, 111702, 
    111701, 111700, 111699, 111698, 111697, 
    111696, 111695, 111694, 111693, 111692, 
    111691, 111690, 111902, 111843, 111684
  ) 
  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 0.00051

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
111684 1.69000000
111690 1.69000000
111691 1.69000000
111692 1.69000000
111693 1.69000000
111694 1.69000000
111695 1.69000000
111696 1.69000000
111697 1.69000000
111698 1.69000000
111699 1.69000000
111700 1.69000000
111701 1.69000000
111702 1.69000000
111703 1.69000000
111704 1.69000000
111705 1.69000000
111706 1.69000000
111843 1.69000000
111902 1.69000000