If those prices are for rust free western buses I would say the prices are in the reasonable price range.
If those prices are for eastern buses I would say those prices are a bit on the high side.
With our height, unless you start with a transit bus that already has considerably more inside height I would say you are going to have to seriously consider raising the roof on any school bus you purchase.
Standard height for school buses has been 74" for many years with 9" windows. From pictures you can tell these buses because the window drip rail will be in a straight line from the top of the driver's window.
Standard height for Crown, Gillig, andIC buses since about 2006 and optional height for the other companies is 78". You can easily tell from pictures which buses these are because the drip rail is several inches above the top of the driver's window.
My last choice in the group of buses you indicated would be the Cat and my first choice would be the DT466. The DT360 is a great little engine with an emphasis on little. Most of the DT360's were in the 160-190 HP range. Most of the DT466's were in the 190-285 HP range.
The Cat is a good engine if it has had all of the updates and recalls. When they work correctly they are a great engine. The problem with them, especially the 3116, is the electronics package can have many bugs that require visits to the Cat dealer for debugging. Figure on $1K per visit.
We currently have four indentical Thomas RE buses that just came out of service that have the Cat 3208. Two of these buses have engines with less than 20K miles on them. All four have the 74" ceiling. 1991 THOMAS RE 3208 1T7A3G908M1777486 - TheBusDealer.com - Auburn, Washington 98001
We also have this one that has quite a few miles but it does have a DT466 that is still very strong. It also has the advantage of having the MT653 (yes that is the 5-speed) with really long highway gears. It can cruise at 70 MPH without any problem. 1990 International BB 1HVBB27N1LH288586 - TheBusDealer.com - Auburn, Washington 98001
And we have this one that has the 12" windows and the DT466. It is a very strong running bus. Asking price is $4,500.00. 1993 IHC BB 1HVBBPGN6PH532355 - TheBusDealer.com - Auburn, Washington 98001
You didn't identify any Cummins powered buses. We have several of those as well.
We have this Blue Bird Type 'D' front engine with a Cummins 5.9L. It has quite a few miles but it is in really good shape and the engine is still running strong. 2001 BLUE BIRD TC2000 1BAAKCPA72F205078 - TheBusDealer.com - Auburn, Washington 98001
And we have this Blue Bird Type 'D' RE commercial bus with pass through luggage compartments under the floor. It has relatively high miles but it has had only highway miles. It has the 8.3L Cummins engine. 1991 Bluebird All-American D Class 1BABLB7A5MF041523 - TheBusDealer.com - Auburn, Washington 98001
Let me know if I can help.
Good luck and happy trails.