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 (
    1288, 1289, 1767, 1347, 665, 581, 299, 
    301, 1799, 1462, 1549, 1521, 1519, 1517, 
    1522, 1523, 1518, 1516, 1520, 30, 31, 
    1545, 1483, 409, 550, 840, 197, 68, 1180, 
    1205
  ) 
  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 0.00151

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": "3",
      "used_key_parts": ["product_id"],
      "rows": 30,
      "filtered": 6.122447491,
      "index_condition": "cscart_product_prices.product_id in (1288,1289,1767,1347,665,581,299,301,1799,1462,1549,1521,1519,1517,1522,1523,1518,1516,1520,30,31,1545,1483,409,550,840,197,68,1180,1205)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}