Originally Posted by SherbetTheShorty
I have a video of the underside also but itís not letting my upload it here. The bus is 2 hours from me, but I looked at it this past weekend. I do recall one part of the floor (about 8-10 inches in size) near the center aisle in the front where the seating starts that sagged a bit when stepped on. Is it safe to assume thatís rusted through then?
Yeah, around the driver's seat is a notorious spot for bad rust. As Rucker said, the rust on the chassis is not a big deal in and of itself, but rust like what you have is a sign that you almost certainly have bad rust going on in the body (the part of the bus above the chassis rails, which includes the floor).
Check out my build thread to see what bad rust can involve. If you're handy with a welder and have access to inexpensive sheet metal, a rusty bus can be a good time. If you don't want to get into fabrication (which will take extra time and money no matter what your skill set), look for a non-rusty bus.