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 (
    7531, 7504, 8342, 8341, 8343, 8344, 8339, 
    8340, 7503, 7539, 7500, 7506, 7669, 
    7530, 7494, 7502, 7501, 8649, 7497, 
    8082, 7932, 7933, 8095, 9387, 7934, 
    7935, 8346, 8349, 8352, 8650, 8348, 
    8350, 8353, 8355, 8347, 8648
  ) 
  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 0.00143

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": 7,
        "filtered": "19.99",
        "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`cscart_product_prices`.`product_id` in (7531,7504,8342,8341,8343,8344,8339,8340,7503,7539,7500,7506,7669,7530,7494,7502,7501,8649,7497,8082,7932,7933,8095,9387,7934,7935,8346,8349,8352,8650,8348,8350,8353,8355,8347,8648))",
        "cost_info": {
          "read_cost": "24.49",
          "eval_cost": "0.72",
          "prefix_cost": "25.21",
          "data_read_per_join": "172"
        },
        "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)))"
      }
    }
  }
}