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 (
    300, 303, 304, 305, 306, 307, 308, 309, 
    310, 311, 312, 313, 314, 315, 316, 298, 
    317, 319, 320, 321, 322, 323, 318, 329, 
    330, 331
  ) 
  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 0.00089

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.00"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "ref",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "lower_limit",
        "used_key_parts": [
          "lower_limit"
        ],
        "key_length": "3",
        "ref": [
          "const"
        ],
        "rows_examined_per_scan": 295,
        "rows_produced_per_join": 6,
        "filtered": "2.19",
        "index_condition": "(`atulecarter_atul_demo1`.`cscart_product_prices`.`lower_limit` <=> 1)",
        "cost_info": {
          "read_cost": "9.00",
          "eval_cost": "1.29",
          "prefix_cost": "68.00",
          "data_read_per_join": "154"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`atulecarter_atul_demo1`.`cscart_product_prices`.`product_id` in (300,303,304,305,306,307,308,309,310,311,312,313,314,315,316,298,317,319,320,321,322,323,318,329,330,331)) and (`atulecarter_atul_demo1`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}