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 (
    325721, 21545, 18228, 163607, 164330, 
    169528, 175066, 184043, 191208, 216438, 
    263004, 279659, 295751, 307166, 308366, 
    315969, 315971, 317489, 317495, 317523, 
    317945, 321995, 321998, 324572
  ) 
  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 0.00177

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "21.63"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "usergroup",
        "used_key_parts": [
          "product_id",
          "usergroup_id",
          "lower_limit"
        ],
        "key_length": "9",
        "rows_examined_per_scan": 48,
        "rows_produced_per_join": 48,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "16.83",
          "eval_cost": "4.80",
          "prefix_cost": "21.63",
          "data_read_per_join": "1K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`unicomps`.`cscart_product_prices`.`lower_limit` = 1) and (`unicomps`.`cscart_product_prices`.`product_id` in (325721,21545,18228,163607,164330,169528,175066,184043,191208,216438,263004,279659,295751,307166,308366,315969,315971,317489,317495,317523,317945,321995,321998,324572)) and (`unicomps`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}