Price depends on your tastes, abilities, and luck. I'm out $2,000 so far and haven't started building - that was just for a roadworthy bus, registration/insurance, and the "parts donor" trailer. That's not including tools, some of which I already had, some of which I had to buy but will be useful for other projects. I'm shooting for under $4,000, but I've only estimated prices of building materials. Of course, none of that cost includes labor - I'm doing everything myself or with free help from friends.
Also, remember fuel - I'm one of the lucky ones that's in double digits (11.4 miles the last time I took her out). A 1,000 mile road trip at 10 mpg is over $300 worth of diesel. Add a few people and that might be reasonable, but I know exactly what it's like to be a broke college student (I'm now a gainfully employed college student
Conventional (nose-in-front) buses are very popular, and often cheaper to buy. They're easy to work on, and most are built on truck chassis with common parts you can get almost anywhere. The downside is that you lose some interior space relative to the overall length. A lot of it is personal preference, so if you like conventionals, that's what you should get.
Most buses were built with standard headroom around 6'1 or 6'2, with an option for "extended headroom" up to 6'5 or 6'6 at the center of the aisle. Remember that insulation and building materials will take away a couple of inches, so look for a high headroom model. The side windows will look taller compared to the height of the entrance door. But of course, you'll be thoroughly checking over any bus before you buy, so stand up inside and make sure you have a couple inches of clearance.