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 (
    366926, 366913, 366931, 366914, 366929, 
    366928, 366927, 366936, 366937, 368738, 
    366940, 366915, 368731, 368839, 366930, 
    368772, 366933, 366934, 368698, 368735
  ) 
  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 0.00146

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "56.07"
    },
    "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": 40,
        "rows_produced_per_join": 40,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "48.07",
          "eval_cost": "8.00",
          "prefix_cost": "56.07",
          "data_read_per_join": "2K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`webmarco`.`cscart_product_prices`.`lower_limit` = 1) and (`webmarco`.`cscart_product_prices`.`product_id` in (366926,366913,366931,366914,366929,366928,366927,366936,366937,368738,366940,366915,368731,368839,366930,368772,366933,366934,368698,368735)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}

Result

product_id price
366913 0.00000000
366914 0.00000000
366915 0.00000000
366926 0.00000000
366927 0.00000000
366928 0.00000000
366929 0.00000000
366930 0.00000000
366931 0.00000000
366933 0.00000000
366934 0.00000000
366936 0.00000000
366937 0.00000000
366940 0.00000000
368698 0.00000000
368731 0.00000000
368735 0.00000000
368738 0.00000000
368772 0.00000000
368839 0.00000000