SELECT 
  q_product_prices.product_id, 
  MIN(
    IF(
      q_product_prices.percentage_discount = 0, 
      q_product_prices.price, 
      q_product_prices.price - (
        q_product_prices.price * q_product_prices.percentage_discount
      )/ 100
    )
  ) AS price 
FROM 
  q_product_prices 
WHERE 
  q_product_prices.product_id IN (
    9661, 9662, 9663, 9664, 9665, 9788, 9874, 
    9875, 9876, 9877, 9878, 9879, 9880, 
    9881, 9882, 9883, 9884, 9885, 9886, 
    9887, 9888, 9889, 9890, 9891, 9892, 
    9893, 9894, 9895, 9896, 9897
  ) 
  AND q_product_prices.lower_limit = 1 
  AND q_product_prices.usergroup_id IN (0, 1) 
GROUP BY 
  q_product_prices.product_id

Query time 0.00095

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "72.01"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "q_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": 30,
        "rows_produced_per_join": 5,
        "filtered": "19.99",
        "index_condition": "(`portal`.`q_product_prices`.`product_id` in (9661,9662,9663,9664,9665,9788,9874,9875,9876,9877,9878,9879,9880,9881,9882,9883,9884,9885,9886,9887,9888,9889,9890,9891,9892,9893,9894,9895,9896,9897))",
        "cost_info": {
          "read_cost": "70.81",
          "eval_cost": "1.20",
          "prefix_cost": "72.01",
          "data_read_per_join": "143"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`portal`.`q_product_prices`.`lower_limit` = 1) and (`portal`.`q_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}