Thing is, that you want to make very big job with very low budget in very short time. It just doesn't add up. You need to change at least one corner of this triangle. Either shrink your project, increase the budget, or accept the fact that it will take very long time to render. Even if xeons will render one frame in 5 minutes, it still will take full 10 days to render your animation.
I'm on a tight budget too, my 5 year old pc renders benchmark in 5 minutes, but i wouldn't ever consider to render 3000 frames interior animation in HD resolution on it. Not with Corona or any other high quality offline renderer. Maybe indeed it's worth to think about real-time engine for your project? Of course that would take huge amount of work and learning new skills if you haven't practise. Anyway, you always need to make compromises between amount of work, budget and timeframe that you have.