Cruzin, the price makes me suspicious, but only because I probably bought my bus from a reseller that marked it up instead of closer to the source. The price may not be so bad, but definitely test drive them. You want to have someone with you as well to look for smoke from the exhaust and listen to / feel the transmission shift. Operate every single control and switch and inspect all of the lighting. A burned out bulb might be more than just the bulb. I had one that was rusted into the socket, causing a short that fed back through one of the main fuse boxes and blew diodes on a circuit board. So that means, headlights on, test blinkers and brakes with the headlights on.
Batteries: if they are dead and the bus needs to be jumped, it might be okay, and it might not be. If the bus needs to be jumped to start it, pop the caps off the batteries and see if there is water in them. Then take a close look at the plates to make sure they aren't bent or warped, or even worse, fused together. Mine were, but I didn't find out until 300 miles down the road when the entire electrical system died a slow death with no blinkers, fading headlights, no brake lights and an unresponsive transmission at 10pm on a Sunday.
As for the mileage, make sure the odometer is actually working. 150k sounds like it's in the right ballpark for the year. Mine is a 2002 with 136k or so. These diesels, if properly maintained, will be just fine up to 400,000 miles so I've heard. Again though, if properly maintained.
If you can find one with a Cummins engine, give that one more points towards your selection (so I've heard.) Mine has a CAT, my buddy's has a Cummins. The Cummins made it home, the CAT didn't, but it really wasn't the engine's fault.
The more thorough you get with your inspection, the better it will be for you. Bring a fuse tester.
Check those tires. Mine had great tread life remaining.
Bring bungie cords, like 10 or more. If the door air system isn't doing so well, you'll want to strap them closed while you drive it home. Again, hopefully not in -20 degree weather.
And, based on the issues I'm dealing with in my shop right now with replacing the radiator, make sure your radiator isn't crumbling.
Many more things, of course. Rust is expected, especially around the wheel wells. Bring a buddy and a chase vehicle, map your route in advance and try to travel during the day and during business hours (maybe not in rush hour traffic), especially if this will be your first heavy vehicle to operate.
My bus is here:
if you want to see some of what I've had to deal with so far. And I still think I did "okay" overall, but my initial cost was $6,000.
I should also say: I am by NO MEANS and expert at all. I've just suffered enough to be able to provide some advice starting out. I'm not a trained mechanic, electrician, carpenter or anything. I'm a tinkerer at most, and a hard-headed one at that. This is my first project of this magnitude ever in my life.