Even if you have no budget you can still do some marketing work of your own. Still worth getting a press release writing even if you do it yourself and getting it out on free wires. Of course should always put the app on appromoter which is free. And there's always social media which can be utilized. Youtube is the second biggest search engine so if you've got a video that can help generate some interest.
Yes, you can put through an update before launching and I believe this might be a way of getting hold of an additional 50 promo codes.
Anyone wants to ask something directly:
alan@appromoter.com or Skype: alanappromoter.
There's a team of us here to answer questions you might have.
Thanks, Alan