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 (
    234552, 218645, 229045, 230883, 233083, 
    233764, 233916, 235216, 591794, 229091, 
    230596, 232944, 233450, 235701, 233529, 
    233637, 229623, 229679, 230360, 230714
  ) 
  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 0.00216

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": "9",
      "used_key_parts": ["product_id", "usergroup_id", "lower_limit"],
      "rowid_filter": {
        "range": {
          "key": "lower_limit",
          "used_key_parts": ["lower_limit", "product_id", "usergroup_id"]
        },
        "rows": 40,
        "selectivity_pct": 0.010320317
      },
      "rows": 40,
      "filtered": 100,
      "index_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.product_id in (234552,218645,229045,230883,233083,233764,233916,235216,591794,229091,230596,232944,233450,235701,233529,233637,229623,229679,230360,230714) and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}