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 (
    415231, 415251, 415216, 415253, 415218, 
    415214, 415333, 415252, 415212, 415344, 
    415204, 415209, 415233, 415207, 415337, 
    415335, 415338, 415222, 415210, 415343
  ) 
  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 0.00152

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 (415231,415251,415216,415253,415218,415214,415333,415252,415212,415344,415204,415209,415233,415207,415337,415335,415338,415222,415210,415343)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}

Result

product_id price
415204 10.00000000
415207 8.00000000
415209 12.00000000
415210 12.00000000
415212 12.00000000
415214 12.00000000
415216 8.00000000
415218 6.00000000
415222 10.00000000
415231 5.00000000
415233 5.00000000
415251 4.00000000
415252 4.00000000
415253 4.00000000
415333 15.00000000
415335 20.00000000
415337 11.00000000
415338 13.00000000
415343 12.00000000
415344 12.00000000