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 (
    2237, 11920, 2184, 2231, 2288, 2346, 
    2348, 2345, 2344, 2350, 2250, 2223, 
    13349, 2355, 2204, 2273, 2278, 2275, 
    2276, 2277, 2272, 2274, 4359, 2326, 
    2251, 2293, 2294, 2295, 2247, 2248
  ) 
  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 0.02153

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_prices.product_id",
      "temporary_table": {
        "table": {
          "table_name": "cscart_product_prices",
          "access_type": "ref",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id"
          ],
          "key": "lower_limit",
          "key_length": "3",
          "used_key_parts": ["lower_limit"],
          "ref": ["const"],
          "rows": 6449,
          "filtered": 7.462925911,
          "attached_condition": "cscart_product_prices.lower_limit <=> 1 and cscart_product_prices.product_id in (2237,11920,2184,2231,2288,2346,2348,2345,2344,2350,2250,2223,13349,2355,2204,2273,2278,2275,2276,2277,2272,2274,4359,2326,2251,2293,2294,2295,2247,2248) and cscart_product_prices.usergroup_id in (0,1)"
        }
      }
    }
  }
}