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 (
    106206, 106040, 105969, 105968, 105777, 
    105776, 105766, 105765, 105721, 105720, 
    105719, 105718, 105717, 104776, 104722, 
    105613, 105612, 105611, 105488, 105487
  ) 
  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 0.00075

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
104722 1.69000000
104776 1.69000000
105487 1.69000000
105488 1.69000000
105611 1.69000000
105612 1.69000000
105613 1.69000000
105717 1.69000000
105718 1.69000000
105719 1.69000000
105720 1.69000000
105721 1.69000000
105765 1.69000000
105766 1.69000000
105776 1.69000000
105777 1.69000000
105968 1.69000000
105969 1.69000000
106040 1.69000000
106206 1.69000000