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 (
    4418, 4421, 4420, 4423, 4600, 5961, 5960, 
    5958, 5959, 1773, 3665, 3666, 4625, 
    5065, 3654, 2237, 3435, 1486, 1083, 
    1231, 1485, 2238, 3427, 3436, 3437, 
    3502, 6072, 3501, 7751, 5603, 6710, 
    4839, 4838, 7593, 7594, 7595, 7596, 
    7597, 7598, 7599, 7600, 6413, 6412, 
    6414, 6415, 6419, 6420, 6418
  ) 
  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 0.00116

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "34.06"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "product_id",
        "used_key_parts": [
          "product_id"
        ],
        "key_length": "3",
        "rows_examined_per_scan": 49,
        "rows_produced_per_join": 9,
        "filtered": "19.12",
        "index_condition": "(`dbggbern`.`cscart_product_prices`.`product_id` in (4418,4421,4420,4423,4600,5961,5960,5958,5959,1773,3665,3666,4625,5065,3654,2237,3435,1486,1083,1231,1485,2238,3427,3436,3437,3502,6072,3501,7751,5603,6710,4839,4838,7593,7594,7595,7596,7597,7598,7599,7600,6413,6412,6414,6415,6419,6420,6418))",
        "cost_info": {
          "read_cost": "33.12",
          "eval_cost": "0.94",
          "prefix_cost": "34.06",
          "data_read_per_join": "224"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`dbggbern`.`cscart_product_prices`.`lower_limit` = 1) and (`dbggbern`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}