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, 366946, 
    366945, 366940, 366909, 366917, 366915, 
    366924, 366910, 366923, 366918, 366919
  ) 
  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 0.00153

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 (366926,366913,366931,366914,366929,366928,366927,366936,366937,366946,366945,366940,366909,366917,366915,366924,366910,366923,366918,366919)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}

Result

product_id price
366909 0.00000000
366910 0.00000000
366913 0.00000000
366914 0.00000000
366915 0.00000000
366917 0.00000000
366918 0.00000000
366919 0.00000000
366923 0.00000000
366924 0.00000000
366926 0.00000000
366927 0.00000000
366928 0.00000000
366929 0.00000000
366931 0.00000000
366936 0.00000000
366937 0.00000000
366940 0.00000000
366945 0.00000000
366946 0.00000000