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 (
    12, 28, 280, 282, 278, 102, 79, 78, 27, 
    11, 41, 7, 34, 38, 15, 80, 31, 81, 109, 
    92, 91, 107
  ) 
  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 0.00005

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_prices.product_id",
      "temporary_table": {
        "table": {
          "table_name": "cscart_product_prices",
          "access_type": "ref",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "lower_limit",
          "key_length": "3",
          "used_key_parts": ["lower_limit"],
          "ref": ["const"],
          "rowid_filter": {
            "range": {
              "key": "product_id",
              "used_key_parts": ["product_id"]
            },
            "rows": 34,
            "selectivity_pct": 13.43873518
          },
          "rows": 234,
          "filtered": 4.886812687,
          "attached_condition": "cscart_product_prices.lower_limit <=> 1 and cscart_product_prices.product_id in (12,28,280,282,278,102,79,78,27,11,41,7,34,38,15,80,31,81,109,92,91,107) and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    }
  }
}