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 (
    101777, 101776, 101775, 101774, 101773, 
    101772, 101771, 101770, 101769, 101768, 
    101767, 101766, 101765, 101764, 101763, 
    101761, 101760, 101759, 101758, 101757
  ) 
  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 0.00067

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
101757 1.69000000
101758 1.69000000
101759 1.69000000
101760 1.69000000
101761 1.69000000
101763 1.69000000
101764 1.69000000
101765 1.69000000
101766 1.69000000
101767 1.69000000
101768 1.69000000
101769 1.69000000
101770 1.69000000
101771 1.69000000
101772 1.69000000
101773 1.69000000
101774 1.69000000
101775 1.69000000
101776 1.69000000
101777 1.69000000