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 (
    51007, 51004, 51005, 51010, 51012, 51013, 
    51011, 51015, 51006, 51021, 51016, 
    51024, 51017, 51019, 51018, 51022, 
    51014, 51045, 51025, 51029, 51027, 
    51020, 51028, 51031, 51042, 51030, 
    51032, 51033, 51026, 51035, 51038, 
    51023
  ) 
  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 0.00074

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "22.41"
    },
    "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": 32,
        "rows_produced_per_join": 6,
        "filtered": "19.96",
        "index_condition": "(`test_uchur_k`.`cscart_product_prices`.`product_id` in (51007,51004,51005,51010,51012,51013,51011,51015,51006,51021,51016,51024,51017,51019,51018,51022,51014,51045,51025,51029,51027,51020,51028,51031,51042,51030,51032,51033,51026,51035,51038,51023))",
        "cost_info": {
          "read_cost": "21.77",
          "eval_cost": "0.64",
          "prefix_cost": "22.41",
          "data_read_per_join": "153"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`test_uchur_k`.`cscart_product_prices`.`lower_limit` = 1) and (`test_uchur_k`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}