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 (
    13774, 11496, 13784, 11492, 11505, 11513, 
    13773, 11495, 13785, 11508, 13777, 
    11494, 11507, 13778, 11502, 11519, 
    11575, 11574, 11506, 13779, 11504, 
    13780, 11501, 13782
  ) 
  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 0.00056

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 (13774,11496,13784,11492,11505,11513,13773,11495,13785,11508,13777,11494,11507,13778,11502,11519,11575,11574,11506,13779,11504,13780,11501,13782)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}

Result

product_id price
11492 319.00000000
11494 109.00000000
11495 199.00000000
11496 205.00000000
11501 135.00000000
11502 155.00000000
11504 179.00000000
11505 399.00000000
11506 159.00000000
11507 215.00000000
11508 125.00000000
11513 165.00000000
11519 159.00000000
11574 999.00000000
11575 999.00000000
13773 156.75000000
13774 84.55000000
13777 118.75000000
13778 204.25000000
13779 151.05000000
13780 170.05000000
13782 128.25000000
13784 194.75000000
13785 189.05000000