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 (
    5783, 5602, 5228, 5969, 5524, 3424, 5558, 
    5559, 5555, 5557, 186, 7032, 7031, 7028, 
    7029, 7030, 7033, 6757, 6759, 6758, 
    3742, 7470, 4038, 3039, 3040, 3420, 
    3461, 3548, 3547, 5077, 5983, 129, 5937, 
    5970, 1824, 7034
  ) 
  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 0.00100

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "25.21"
    },
    "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": 36,
        "rows_produced_per_join": 6,
        "filtered": "19.12",
        "index_condition": "(`dbggbern`.`cscart_product_prices`.`product_id` in (5783,5602,5228,5969,5524,3424,5558,5559,5555,5557,186,7032,7031,7028,7029,7030,7033,6757,6759,6758,3742,7470,4038,3039,3040,3420,3461,3548,3547,5077,5983,129,5937,5970,1824,7034))",
        "cost_info": {
          "read_cost": "24.52",
          "eval_cost": "0.69",
          "prefix_cost": "25.21",
          "data_read_per_join": "165"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`dbggbern`.`cscart_product_prices`.`lower_limit` = 1) and (`dbggbern`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}