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 (
    81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 
    92, 93, 94, 95, 96, 97, 100, 101, 102, 
    103, 104, 105, 106, 107, 108, 109, 110, 
    111, 112, 113, 114
  ) 
  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 0.00378

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.065680453,
    "filesort": {
      "sort_key": "cscart_product_prices.product_id",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_product_prices",
              "access_type": "ALL",
              "possible_keys": [
                "usergroup",
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "loops": 1,
              "rows": 253,
              "cost": 0.0520938,
              "filtered": 8.39881897,
              "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.product_id in (81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114) and cscart_product_prices.usergroup_id in (0,1)"
            }
          }
        ]
      }
    }
  }
}