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 (
    421, 443, 1971, 1959, 1960, 436, 438, 
    437, 1961, 1931, 381, 1529, 1465, 1962, 
    1933, 1935, 1958, 428, 406, 439, 390, 
    1969, 398, 1964, 434, 383, 435, 419, 
    403, 324, 1965, 440, 1966, 431, 1973, 
    1968, 1963, 327, 1934, 385, 405, 413, 
    1970, 1937, 433, 414, 407, 402, 1972, 
    388, 1974, 442, 1936, 416, 326, 441, 
    1957
  ) 
  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 0.00334

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "153.61"
    },
    "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": 69,
        "rows_produced_per_join": 13,
        "filtered": "19.98",
        "index_condition": "(`eshopuga_upgr_4122`.`cscart_product_prices`.`product_id` in (421,443,1971,1959,1960,436,438,437,1961,1931,381,1529,1465,1962,1933,1935,1958,428,406,439,390,1969,398,1964,434,383,435,419,403,324,1965,440,1966,431,1973,1968,1963,327,1934,385,405,413,1970,1937,433,414,407,402,1972,388,1974,442,1936,416,326,441,1957))",
        "cost_info": {
          "read_cost": "150.85",
          "eval_cost": "2.76",
          "prefix_cost": "153.61",
          "data_read_per_join": "330"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`eshopuga_upgr_4122`.`cscart_product_prices`.`lower_limit` = 1) and (`eshopuga_upgr_4122`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}