We paid a amount of money asked that was at the contract to our lawyer . After I filled the waiver the government now wants more evidences in 30 days .
The lawyer is asking for 2500 fee more to send the evidences to the government . Is this the way it is?

This is the way it is... and it might take a lot more time and a lot more money before its done. Every case is different, some take a lot more. Once in a while you might spend well over $10,000 and over ten years only to be refused entry. There are no guarantees.

Time is money...Lawyers get paid for their time..the longer it takes and the more of their time it takes the more you will pay.

It depends, most immigration attorneys in US charge flat rate fees. Read your contract agreement and see if this is mentioned in the contract. If not, clients have to pay for additional services.