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 (
    192, 230, 231, 232, 233, 234, 235, 236, 
    237, 238, 239, 193, 240, 241, 242, 243, 
    194, 195, 198, 199
  ) 
  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 0.00077

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_prices",
      "access_type": "ref",
      "possible_keys": ["usergroup", "product_id", "lower_limit", "usergroup_id"],
      "key": "lower_limit",
      "key_length": "3",
      "used_key_parts": ["lower_limit"],
      "ref": ["const"],
      "rows": 40,
      "filtered": 31.74603081,
      "index_condition": "cscart_product_prices.product_id in (192,230,231,232,233,234,235,236,237,238,239,193,240,241,242,243,194,195,198,199) and cscart_product_prices.usergroup_id in (0,1)",
      "attached_condition": "cscart_product_prices.lower_limit <=> 1"
    }
  }
}