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 (
    12684, 12685, 12686, 12687, 12688, 12689, 
    12690, 12691, 12692, 12693, 12694, 
    12695, 12696, 12697, 12698, 12699, 
    12700, 12701, 12702, 12703, 12704, 
    12705, 12706, 12707, 12708, 12709, 
    12710, 12711, 12712, 12713
  ) 
  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 0.06400

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "42.01"
    },
    "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": 60,
        "rows_produced_per_join": 60,
        "filtered": "100.00",
        "index_condition": "((`test2_gaseus`.`cscart_product_prices`.`lower_limit` = 1) and (`test2_gaseus`.`cscart_product_prices`.`product_id` in (12684,12685,12686,12687,12688,12689,12690,12691,12692,12693,12694,12695,12696,12697,12698,12699,12700,12701,12702,12703,12704,12705,12706,12707,12708,12709,12710,12711,12712,12713)) and (`test2_gaseus`.`cscart_product_prices`.`usergroup_id` in (0,1)))",
        "cost_info": {
          "read_cost": "36.01",
          "eval_cost": "6.00",
          "prefix_cost": "42.01",
          "data_read_per_join": "1K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ]
      }
    }
  }
}