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 (
    101823, 101822, 101821, 101820, 101819, 
    101818, 101817, 101816, 101815, 101814, 
    101813, 101714, 101713, 101643, 101642, 
    101641, 101640, 101639, 101218, 101217
  ) 
  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 0.00057

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
101217 1.69000000
101218 1.69000000
101639 1.69000000
101640 1.69000000
101641 1.69000000
101642 1.69000000
101643 1.69000000
101713 1.69000000
101714 1.69000000
101813 1.69000000
101814 1.69000000
101815 1.69000000
101816 1.69000000
101817 1.69000000
101818 1.69000000
101819 1.69000000
101820 1.69000000
101821 1.69000000
101822 1.69000000
101823 1.69000000