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 (
    11509, 13776, 11511, 11521, 11527, 11489, 
    11524, 11497, 11510, 13775, 11515, 
    13772, 11486, 11487, 11520, 11503, 
    13781, 11548, 11547, 11549, 11573, 
    11493, 11490, 11512
  ) 
  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 0.00057

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": 24,
      "filtered": 100,
      "index_condition": "cscart_product_prices.product_id in (11509,13776,11511,11521,11527,11489,11524,11497,11510,13775,11515,13772,11486,11487,11520,11503,13781,11548,11547,11549,11573,11493,11490,11512)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}

Result

product_id price
11486 350.00000000
11487 350.00000000
11489 79.00000000
11490 95.00000000
11493 199.00000000
11497 145.00000000
11503 699.00000000
11509 105.00000000
11510 60.00000000
11511 115.00000000
11512 89.00000000
11515 145.00000000
11520 59.00000000
11521 159.00000000
11524 139.00000000
11527 159.00000000
11547 109.00000000
11548 109.00000000
11549 109.00000000
11573 8999.00000000
13772 137.75000000
13775 57.00000000
13776 99.75000000
13781 664.05000000