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 (
    282971, 286602, 283081, 283125, 286561, 
    282507, 283098, 279396, 286611, 282889, 
    282945, 286621, 277944, 286500, 286533, 
    284472, 286574, 279355, 278025, 278209, 
    285797, 279438, 270384, 281368, 270320, 
    286493, 277872, 286557, 278250, 278190, 
    285798, 285799, 285796, 285794, 286704, 
    281369
  ) 
  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 0.00236

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "100.92"
    },
    "grouping_operation": {
      "using_filesort": false,
      "table": {
        "table_name": "cscart_product_prices",
        "access_type": "range",
        "possible_keys": [
          "usergroup",
          "product_id",
          "lower_limit",
          "usergroup_id"
        ],
        "key": "usergroup",
        "used_key_parts": [
          "product_id",
          "usergroup_id",
          "lower_limit"
        ],
        "key_length": "9",
        "rows_examined_per_scan": 72,
        "rows_produced_per_join": 72,
        "filtered": "100.00",
        "cost_info": {
          "read_cost": "86.52",
          "eval_cost": "14.40",
          "prefix_cost": "100.92",
          "data_read_per_join": "4K"
        },
        "used_columns": [
          "product_id",
          "price",
          "percentage_discount",
          "lower_limit",
          "usergroup_id"
        ],
        "attached_condition": "((`webmarco`.`cscart_product_prices`.`lower_limit` = 1) and (`webmarco`.`cscart_product_prices`.`product_id` in (282971,286602,283081,283125,286561,282507,283098,279396,286611,282889,282945,286621,277944,286500,286533,284472,286574,279355,278025,278209,285797,279438,270384,281368,270320,286493,277872,286557,278250,278190,285798,285799,285796,285794,286704,281369)) and (`webmarco`.`cscart_product_prices`.`usergroup_id` in (0,1)))"
      }
    }
  }
}