Check this out, Google are giving away free credit for GCE here:
https://cloud.google.com/resources/starterpack/
I just received mine earlier. It's an easy process: just fill in their form, once you get an email saying you've been selected, add a project to your account and enable billing (on both GAE and GCE), fill in another form, and you'll get the credits.
$1000 is enough to run a standard instance 24/7 for 6 months, but you can do whatever with it. Pricing is here: https://cloud.google.com/pricing/compute-engine
For the promo code in the application, you can use swsoc-org (found it on a company's Facebook page).