I have talked with bus barn service guys in a district that ran a number of G3500's. They were quite happy with them. Different motor but they liked the platform.
The 6.5 has it's haters. I have been around several of them and am of the opinion that they are a very reliable and economical engines. But...,... If you are ever in a hurry to get somewhere...... Buy something else...
Regarding price, I think that $5k for that bus may be on the high side. I see similar buses for quite a bit less.