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 (
    1668, 1669, 1670, 1671, 2220, 2221, 2222, 
    2223, 5353, 5354, 5355, 5356, 5357, 
    5358, 5359, 5360, 5361, 5362, 5363, 
    5364, 5365, 5366, 5367, 5368, 5369, 
    5370, 5820, 5821, 5822, 5823, 12916, 
    12921, 12876, 12896, 12900, 12909
  ) 
  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 0.00094

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "38.71"
    },
    "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": 66,
        "rows_produced_per_join": 13,
        "filtered": "19.99",
        "index_condition": "(`test2_gaseus`.`cscart_product_prices`.`product_id` in (1668,1669,1670,1671,2220,2221,2222,2223,5353,5354,5355,5356,5357,5358,5359,5360,5361,5362,5363,5364,5365,5366,5367,5368,5369,5370,5820,5821,5822,5823,12916,12921,12876,12896,12900,12909))",
        "cost_info": {
          "read_cost": "37.39",
          "eval_cost": "1.32",
          "prefix_cost": "38.71",
          "data_read_per_join": "316"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`test2_gaseus`.`cscart_product_prices`.`lower_limit` = 1) and (`test2_gaseus`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}