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 (
    51033, 51026, 51035, 51059, 51069, 51070, 
    51038, 51066, 51023, 51041, 51056, 
    51040, 51050, 51065, 51039, 51052, 
    51009, 51034, 51061, 51036, 51037, 
    51068, 51064, 51055, 51058, 51071
  ) 
  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 0.00097

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "18.21"
    },
    "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": 26,
        "rows_produced_per_join": 5,
        "filtered": "19.96",
        "index_condition": "(`test_uchur_k`.`cscart_product_prices`.`product_id` in (51033,51026,51035,51059,51069,51070,51038,51066,51023,51041,51056,51040,51050,51065,51039,51052,51009,51034,51061,51036,51037,51068,51064,51055,51058,51071))",
        "cost_info": {
          "read_cost": "17.69",
          "eval_cost": "0.52",
          "prefix_cost": "18.21",
          "data_read_per_join": "124"
        },
        "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)))"
      }
    }
  }
}