'06 525i No dash lights or start

[Iconrider]

I’m new here so Hoping I’m posting in the right forum…

I am looking at purchasing a car for my daughter and I found a 2006 525i that, at first glance, appears to be in decent enough shape but is having an ignition problem that I’m not familiar with. I have a 2006 325i I purchased for my son and tore into it pretty deep to get it up to par so I know what to look for on the surface, but never had electrical issues.

So the key fob will lock and unlock the doors, pop the trunk, the power seats both work, and the power steering column works. But when you put the key in the ignition and press the start button, nothing happens. No dash lights, no iDrive, nothing. The seller believes it to be a bad transponder in the key fob but all the research I’ve done on that seems like I would at least get the dash to come on but the car just wouldn’t start if it was bad. This does have the key with the removable battery and I tried a new battery in it but that had no effect.

Any suggestions before I simply walk away from what might be a good deal?