A 5-6 window bus is an awfully small bus. The interior volume is going to be less than most Class 'C' motorhomes but a little more than most Class 'B' motorhomes. Most short school buses also have lower ceilings which cuts down on the interior volume some more. The other real problem with short buses is the same problem most Class 'A', Class 'B' and Class 'C' motorhomes have--there is always more bus on top than there is truck underneath to carry the weight. The translation is wear items like brakes, suspension parts, and tires wear out considerably more often than large buses and large Class 'A' motorhomes.
The use for which you will be using your bus is sort of important as well.
If you want to do lots of interstate travel then most school buses are really not the best choice of bus to convert.
If you are wanting to get off the beaten track, travel the back roads, and never go very far at any one time then the right converted school bus may be the best bus to convert.
So before you start shopping for used buses you need to decide what exactly you need, how much space you need, and what sort of budget you have to accomplish your conversion.
This link will take you to one of the nicest conversions of a small bus I have ever seen.
http://cgi.ebay.com/ebaymotors/1949-Flx ... 4cf6cfc544 (and if Rudy could capture the pictures and put them in the older motorhome section that would be great!) By the price you can see how much nice is going to cost.
As far as shopping for buses is concerned, once you have determined what size of bus you want then you have to decide what parameters in regards to body make, power package, and chassis at which you will look. In this respect a lot of Ford vs. Chevy issues will play in the determining factor. I personally do not like Blue Bird bodies even though Blue Bird makes a very good bus body. My reasons for not liking Blue Bird are rather petty but there you go.
In regards to how far you will go to get a bus, it all depends upon price. At $5.00 per gallon your fuel cost for transporting a bus from wherever to your home will cost about $0.60 per mile just for fuel. Add the cost of you getting from your home to where the bus is and you will be able to get a good idea of what an expensive bus close by is worth compared to a really inexpensive bus 2000 miles away.
The most expensive part of a conversion is the power package. Always, and I mean ALWAYS, opt for the bus with the better power package. It will save time and $$$ down the road.
The next most expensive part of a conversion is rust repair. If there is any body rust, unless you are being paid to take it away, don't bother.
The least important part of a purchase of an uncoverted bus will be the tires. As long as they are legal and will get you home that is all you will need. There is no reason to pay extra $$$ for tires now that will most likely need to be replaced after your conversion is completed. Tires have a shelf life and will deteriorate just sitting around. I had to throw away a set of tires with a documented mileage of less than 12,000 miles. They were almost ten years old and died of old age, not wear.
If at this point you are still wanting to convert a bus start reading up about RV plumbing, electrical, heating/cooling, and bus maintenance/repair. The more you know the less you will have to pay. Think in terms of shop time to repair a bus in excess of $105.00 per hour and RV repair just about as expensive.
And if this hasn't scared you away, keep us posted and we will help you as much as we can.
Good luck.