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 (
    36474, 4237, 43798, 5270, 5257, 6070, 
    37849, 335, 5726, 41437, 5288, 40809, 
    5228, 37881, 18194, 37300, 4795, 5265, 
    40309, 6371, 38150, 40754, 4279, 47652, 
    37296, 5770, 26849, 31734, 27056, 37294, 
    40807, 41358
  ) 
  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 0.00344

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 (36474,4237,43798,5270,5257,6070,37849,335,5726,41437,5288,40809,5228,37881,18194,37300,4795,5265,40309,6371,38150,40754,4279,47652,37296,5770,26849,31734,27056,37294,40807,41358)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}