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 (
    6290, 6085, 6016, 6017, 6084, 6191, 6018, 
    6086, 6081, 6144, 6254, 6228, 6192, 
    6227, 6083, 6230, 6275, 6277, 6291, 
    6258, 6255, 6229, 6256, 6189, 6257, 
    6259, 6145, 6226, 6279, 6278, 6190, 
    6276, 6280, 6260, 6274, 6281, 6282
  ) 
  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 0.00209

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "25.91"
    },
    "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": 37,
        "rows_produced_per_join": 7,
        "filtered": "19.99",
        "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`product_id` in (6290,6085,6016,6017,6084,6191,6018,6086,6081,6144,6254,6228,6192,6227,6083,6230,6275,6277,6291,6258,6255,6229,6256,6189,6257,6259,6145,6226,6279,6278,6190,6276,6280,6260,6274,6281,6282))",
        "cost_info": {
          "read_cost": "25.17",
          "eval_cost": "0.74",
          "prefix_cost": "25.91",
          "data_read_per_join": "177"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`lower_limit` = 1) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}