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 (
    38074, 6357, 5503, 17265, 5990, 34555, 
    31638, 31633, 31632, 5300, 5991, 5297, 
    1980, 1103, 31634, 31631, 1102, 31636, 
    1104, 1979, 17259, 398, 1981, 1716, 
    31637, 5278, 1277, 31635, 1580, 121, 
    120, 43824
  ) 
  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 0.00279

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_prices",
          "access_type": "range",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "product_id",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "rows": 32,
          "filtered": 99.9960556,
          "index_condition": "cscart_product_prices.product_id in (38074,6357,5503,17265,5990,34555,31638,31633,31632,5300,5991,5297,1980,1103,31634,31631,1102,31636,1104,1979,17259,398,1981,1716,31637,5278,1277,31635,1580,121,120,43824)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}