Well, best way is to try by yourself. Appointments are made available mostly during noon time between 11am to 1 pm EST. You have to refresh the NVARS page every minute.
If you can not make it, it's better to pay, some one else will do it for you.
Here is one link that you can use, I was also in similar situation and found out about this web site, however I did not use it as I got appointment by myself.

http://www.gtasaving.com/usvisa2

I hope it helps you. It was the cheapest one I found.

Good luck.