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 (
    389621, 389620, 389623, 389624, 389622, 
    389626, 389627, 389625, 282478, 282479, 
    391683, 308674, 308677, 392154, 308679, 
    392152, 392156, 308675, 392155, 308680, 
    308678, 392157, 308673, 392158, 308676, 
    392153
  ) 
  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 0.00158

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "72.89"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "usergroup",
        "used_key_parts": [
          "product_id",
          "usergroup_id",
          "lower_limit"
        ],
        "key_length": "9",
        "rows_examined_per_scan": 52,
        "rows_produced_per_join": 52,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "62.49",
          "eval_cost": "10.40",
          "prefix_cost": "72.89",
          "data_read_per_join": "3K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`webmarco`.`cscart_product_prices`.`lower_limit` = 1) and (`webmarco`.`cscart_product_prices`.`product_id` in (389621,389620,389623,389624,389622,389626,389627,389625,282478,282479,391683,308674,308677,392154,308679,392152,392156,308675,392155,308680,308678,392157,308673,392158,308676,392153)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}