I'd like to help but you did not mention the end of the licence date?
For indepth-details for MS licence subscriptions, see this. Also this QA topic suggests it is free.
On another note, do you think it you are much less competitive by using the free Visual Studio (2012) Express Editions.The IDE is pretty similar, as are the shortcuts. Am I correct in the assumption that this event is a few-hours long Hackathon ?
In fact, you may just as well use MonoDevelop and probably still be highly competitive based on other merits than your proficiency in a given IDE.
I hope this helps.