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 (
    50216, 50194, 40927, 6372, 6358, 6357, 
    31633, 1975, 2305, 49192, 2303, 6354, 
    31965, 26895, 26894, 38797, 26872, 
    47567, 26871, 26876, 26870, 26874, 
    26878, 26885, 26875, 26879, 26884, 
    1972, 44424, 5141, 297, 51
  ) 
  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 0.00415

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "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": 32,
          "filtered": 99.9960556,
          "index_condition": "cscart_product_prices.product_id in (50216,50194,40927,6372,6358,6357,31633,1975,2305,49192,2303,6354,31965,26895,26894,38797,26872,47567,26871,26876,26870,26874,26878,26885,26875,26879,26884,1972,44424,5141,297,51)",
          "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    ]
  }
}