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 (
    11887, 11909, 11929, 11936, 11940, 11944, 
    11951, 11958, 11959, 11960, 11961, 
    11962, 11963, 11964, 11965, 12030, 
    12031, 12032, 12033, 12034, 12035, 
    12036, 12037, 12102, 12116, 12118, 
    12132, 12146, 12160, 12174, 12188, 
    12202, 8203, 8214, 8215, 8216, 8217, 
    8218, 8205, 8206, 8207, 8208, 8209, 
    8210, 8211, 8212
  ) 
  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 0.00079

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "38.06"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_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": 59,
        "rows_produced_per_join": 11,
        "filtered": "20.00",
        "index_condition": "(`gaseus`.`cscart_product_prices`.`product_id` in (11887,11909,11929,11936,11940,11944,11951,11958,11959,11960,11961,11962,11963,11964,11965,12030,12031,12032,12033,12034,12035,12036,12037,12102,12116,12118,12132,12146,12160,12174,12188,12202,8203,8214,8215,8216,8217,8218,8205,8206,8207,8208,8209,8210,8211,8212))",
        "cost_info": {
          "read_cost": "36.88",
          "eval_cost": "1.18",
          "prefix_cost": "38.06",
          "data_read_per_join": "283"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`gaseus`.`cscart_product_prices`.`lower_limit` = 1) and (`gaseus`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}