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 (
    4078, 5006, 4116, 5076, 4136, 4133, 4219, 
    4115, 4127, 4121, 4120, 4087, 4122, 
    4129, 4119, 4126, 4086, 4118, 4117, 
    4084, 4128, 4080, 4079, 4132
  ) 
  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 0.00059

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": "3",
      "used_key_parts": ["product_id"],
      "rows": 49,
      "filtered": 97.95918274,
      "index_condition": "cscart_product_prices.product_id in (4078,5006,4116,5076,4136,4133,4219,4115,4127,4121,4120,4087,4122,4129,4119,4126,4086,4118,4117,4084,4128,4080,4079,4132)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}