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 (
    65438, 65436, 65439, 65432, 65450, 65451, 
    65433, 65472, 65448, 65434, 65452, 
    65441, 65435, 65476, 65475, 65477, 
    65473, 65956, 65891
  ) 
  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 0.00143

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_prices",
      "access_type": "range",
      "possible_keys": ["usergroup", "product_id", "lower_limit", "usergroup_id"],
      "key": "product_id",
      "key_length": "9",
      "used_key_parts": ["product_id", "usergroup_id", "lower_limit"],
      "rowid_filter": {
        "range": {
          "key": "lower_limit",
          "used_key_parts": ["lower_limit", "product_id", "usergroup_id"]
        },
        "rows": 38,
        "selectivity_pct": 1.408450704
      },
      "rows": 38,
      "filtered": 100,
      "index_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.product_id in (65438,65436,65439,65432,65450,65451,65433,65472,65448,65434,65452,65441,65435,65476,65475,65477,65473,65956,65891) and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}

Result