not completely true

if a contract violates the law, it is void. in this case, if the agreement does specifically say about the cost of H-1B application, it could be an issue.

however, I'd say just pay that cost since it is not a huge amount, and the company hired you in good faith and you signed it in good faith. otherwise the company may shut the door for any further H-1B new hires.

be nice to other ppl if they treat you nicely.