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 (
    238400, 238518, 258627, 279059, 322596, 
    10101, 141331, 182500, 183418, 210394, 
    216091, 216439, 244556, 285152, 304053, 
    311249, 326960, 154729, 163659, 183540, 
    200612, 255788, 255803, 274116
  ) 
  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 0.00199

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "21.63"
    },
    "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": 48,
        "rows_produced_per_join": 48,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "16.83",
          "eval_cost": "4.80",
          "prefix_cost": "21.63",
          "data_read_per_join": "1K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`unicomps`.`cscart_product_prices`.`lower_limit` = 1) and (`unicomps`.`cscart_product_prices`.`product_id` in (238400,238518,258627,279059,322596,10101,141331,182500,183418,210394,216091,216439,244556,285152,304053,311249,326960,154729,163659,183540,200612,255788,255803,274116)) and (`unicomps`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}