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 (
    6432, 6433, 6434, 6435, 6436, 6437, 6438, 
    6439, 6440, 6441, 6442, 6443, 6444, 
    6445, 6446, 6447, 6526, 6527, 6528, 
    6529, 6530, 6531, 6532, 6533, 6534, 
    6615, 6616, 6617, 6618, 6619, 6620, 
    6621, 6622, 2272, 2273, 2274, 2275, 
    2276, 2340, 2341, 2342, 2343, 2344, 
    2345, 2346, 2347, 2348, 2421
  ) 
  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 0.00097

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "34.06"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "product_id",
        "used_key_parts": [
          "product_id"
        ],
        "key_length": "3",
        "rows_examined_per_scan": 49,
        "rows_produced_per_join": 9,
        "filtered": "20.00",
        "index_condition": "(`gaseus`.`cscart_product_prices`.`product_id` in (6432,6433,6434,6435,6436,6437,6438,6439,6440,6441,6442,6443,6444,6445,6446,6447,6526,6527,6528,6529,6530,6531,6532,6533,6534,6615,6616,6617,6618,6619,6620,6621,6622,2272,2273,2274,2275,2276,2340,2341,2342,2343,2344,2345,2346,2347,2348,2421))",
        "cost_info": {
          "read_cost": "33.08",
          "eval_cost": "0.98",
          "prefix_cost": "34.06",
          "data_read_per_join": "235"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`gaseus`.`cscart_product_prices`.`lower_limit` = 1) and (`gaseus`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}