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 (
    1720, 1719, 1718, 1717, 1716, 1715, 1714, 
    1713, 1711, 1710, 1709, 1708, 1707, 
    1706, 1705, 1704, 1703, 1702, 1701, 
    1700, 1699, 1698, 1697, 1696
  ) 
  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 0.00115

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": 24,
      "filtered": 4.897957802,
      "index_condition": "cscart_product_prices.product_id in (1720,1719,1718,1717,1716,1715,1714,1713,1711,1710,1709,1708,1707,1706,1705,1704,1703,1702,1701,1700,1699,1698,1697,1696)",
      "attached_condition": "cscart_product_prices.lower_limit = 1 and cscart_product_prices.usergroup_id in (0,1)"
    }
  }
}