The highest amount is limited by your bank. Normally, <10K, the service fee is same. Some banks have a little difference, for example, Eastern Bank in NYC, $12 (<3K), $16 (3K to 10K), $20 (>=10K).
If you are not in a hurry, I suggest you send your personal check. But, you have to make sure your check is cashable in one of the bank in China (normally Bank of China).
If you are not in a hurry, I suggest you send your personal check. But, you have to make sure your check is cashable in one of the bank in China (normally Bank of China).