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 (
    4725, 4726, 4735, 4024, 4020, 4028, 4037, 
    4019, 4029, 4036, 4740, 4739, 4928, 
    4493, 4495, 4496, 4494, 4909
  ) 
  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 0.00054

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": "range",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "usergroup_id",
          "key_length": "6",
          "used_key_parts": ["usergroup_id", "product_id"],
          "rows": 36,
          "filtered": 100,
          "index_condition": "cscart_product_prices.product_id in (4725,4726,4735,4024,4020,4028,4037,4019,4029,4036,4740,4739,4928,4493,4495,4496,4494,4909) and cscart_product_prices.usergroup_id in (0,1)",
          "attached_condition": "cscart_product_prices.lower_limit = 1"
        }
      }
    }
  }
}