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 (
    7249, 7247, 7243, 7248, 7246, 7244, 7242, 
    7245, 6692, 6702, 6703, 6704, 6705, 
    6707, 6708, 6706, 5704, 1297, 1301, 
    1298, 1299, 1296, 1294, 1300
  ) 
  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 0.00044

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "16.81"
    },
    "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": 24,
        "rows_produced_per_join": 4,
        "filtered": "19.12",
        "index_condition": "(`dbggbern`.`cscart_product_prices`.`product_id` in (7249,7247,7243,7248,7246,7244,7242,7245,6692,6702,6703,6704,6705,6707,6708,6706,5704,1297,1301,1298,1299,1296,1294,1300))",
        "cost_info": {
          "read_cost": "16.35",
          "eval_cost": "0.46",
          "prefix_cost": "16.81",
          "data_read_per_join": "110"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`dbggbern`.`cscart_product_prices`.`lower_limit` = 1) and (`dbggbern`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}