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 (
    8633, 8583, 8657, 8408, 8409, 10177, 
    8405, 8406, 9943, 16031, 54977, 8407, 
    8649, 36024, 36027, 26947, 36025, 26577, 
    34036, 30720, 12085, 26543, 26539, 
    31010, 39503, 12086, 40547, 40112, 
    40580, 12088, 40714, 33996, 12087, 
    26542, 36036, 33791, 40836, 40232, 
    40208, 40469, 40616, 26537, 40738, 
    36041, 40374, 40088, 40787, 40679, 
    40516, 40350
  ) 
  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 0.00169

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "35.01"
    },
    "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": 50,
        "rows_produced_per_join": 9,
        "filtered": "20.00",
        "index_condition": "(`cscartdb`.`cscart_product_prices`.`product_id` in (8633,8583,8657,8408,8409,10177,8405,8406,9943,16031,54977,8407,8649,36024,36027,26947,36025,26577,34036,30720,12085,26543,26539,31010,39503,12086,40547,40112,40580,12088,40714,33996,12087,26542,36036,33791,40836,40232,40208,40469,40616,26537,40738,36041,40374,40088,40787,40679,40516,40350))",
        "cost_info": {
          "read_cost": "34.01",
          "eval_cost": "1.00",
          "prefix_cost": "35.01",
          "data_read_per_join": "239"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`cscartdb`.`cscart_product_prices`.`lower_limit` = 1) and (`cscartdb`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}