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 (
    100177, 99746, 99740, 99739, 99738, 
    99737, 99736, 99735, 93037, 100224, 
    100223, 100222, 100221, 100220, 100219, 
    100218, 100217, 100216, 100215, 100214
  ) 
  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 0.00078

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
93037 1.69000000
99735 1.69000000
99736 1.69000000
99737 1.69000000
99738 1.69000000
99739 1.69000000
99740 1.69000000
99746 1.69000000
100177 1.69000000
100214 1.69000000
100215 1.69000000
100216 1.69000000
100217 1.69000000
100218 1.69000000
100219 1.69000000
100220 1.69000000
100221 1.69000000
100222 1.69000000
100223 1.69000000
100224 1.69000000