SELECT 
  cscart_ult_product_prices.product_id, 
  MIN(
    IF(
      cscart_ult_product_prices.percentage_discount = 0, 
      cscart_ult_product_prices.price, 
      cscart_ult_product_prices.price - (
        cscart_ult_product_prices.price * cscart_ult_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  cscart_ult_product_prices 
WHERE 
  cscart_ult_product_prices.product_id IN (
    70121, 70812, 70727, 70339, 70697, 70696, 
    70695, 70694, 70640, 70600, 70584, 
    70539, 70432, 70357, 70587, 70586, 
    70583, 70579, 70537, 70493, 70120, 
    69978, 69977, 70358, 70462, 70459, 
    70458, 70433, 69982, 70435, 70434, 
    70362, 70015, 70014, 70235, 70234, 
    70161, 70119, 69980, 69745
  ) 
  AND cscart_ult_product_prices.lower_limit = 1 
  AND cscart_ult_product_prices.company_id = 1 
  AND cscart_ult_product_prices.usergroup_id IN (0, 0, 1) 
GROUP BY 
  cscart_ult_product_prices.product_id

Query time 0.00049

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE cscart_ult_product_prices range usergroup,product_id,company_id,lower_limit,usergroup_id usergroup 13 1 Using where