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 (
    474, 426, 793, 794, 1147, 849, 850, 852, 
    853, 851, 855, 854, 856, 208, 209, 210, 
    886, 555, 630, 554, 1109, 320, 318, 319, 
    969, 970, 252, 454, 639, 49
  ) 
  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 0.00137

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": 30,
      "filtered": 6.122447491,
      "index_condition": "cscart_product_prices.product_id in (474,426,793,794,1147,849,850,852,853,851,855,854,856,208,209,210,886,555,630,554,1109,320,318,319,969,970,252,454,639,49)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}