You can definitely pull this off on a budget. People regularly throw away (almost) everything you'll need to make this happen. Watch the craigslist free section like a hawk. Consider posting there too, explaining what you're doing and politely asking for help from anyone who might have materials or help for you. Check your local landfill. Talk to contractors and tell them about your project. You can likely get scrap wood, full kitchen tear outs (all the old cabinets when they do a remodel,) appliances, etc.
If you are patient and resourceful, the conversion doesn't need to cost much, especially just to get to the point you can insure it as an rv. And you said you have a place to store it, so you don't even need insurance for a while until its ready to roll.
Doing everything "all at once" is usually the most expensive route. Because instead of waiting for things to pop up at the right price (free) you end up going out to home depot and paying retail. If you can take your time, you'll find most of what you need second hand.
Make sure your friends who plan to enjoy the bus with you actually contribute something to its reality, be it money or time. I'm in a similar age demographic/situation and there are lots of people who will try to free-load off you once all the hard work is done. Beware, just not jaded, people are what they are.
http://www.skoolie.net/forums/showthread.php?t=9883 - 7.3L 4x4 Shuttle Bus Toyhauler conversion