SELECT 
  MIN(price) AS min_price, 
  MAX(price) AS max_price 
FROM 
  cscart_product_prices 
WHERE 
  product_id IN (12, 286)

Query time 0.00033

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.21"
    },
    "table": {
      "table_name": "cscart_product_prices",
      "access_type": "range",
      "possible_keys": [
        "usergroup",
        "product_id"
      ],
      "key": "usergroup",
      "used_key_parts": [
        "product_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 3,
      "rows_produced_per_join": 3,
      "filtered": "100.00",
      "index_condition": "(`atulecarter_new_april_setup`.`cscart_product_prices`.`product_id` in (12,286))",
      "cost_info": {
        "read_cost": "5.61",
        "eval_cost": "0.60",
        "prefix_cost": "6.21",
        "data_read_per_join": "72"
      },
      "used_columns": [
        "product_id",
        "price"
      ]
    }
  }
}