In some folks minds, any rust is too much rust!
I can tell you that the rust you see, is likely not the only rust on the undercarriage.
Closer inspection is really needed, to include a screwdriver test around wheel wells and any other place that flaky rust is visible.
If the screwdriver penetrates more that 2 places under the floor, I'd pass on that bus and keep looking.
On a more positive note, the engine looks fairly clean for having 160K on it.