2 Answers

I didn't think it was illegal- But, i looked it up and yes! It's illegal to have anything that an officer considers an obstruction to view is ticketable.  However, Ironically if you mount it to your visor and pull it down in front of you its not illegal.  technicality-- And as I further investigate this, the courts are aware of this minor technicality so even though its against the law, the usually throw it out.  Police officers won't even waste their time on it.    But, for reasonable safety, you probably shouldn't place it on the windshield, just mount it on the visor or dash.  And don't assume that I am the last word, I am only passing on what I read.  What I read could be wrong and you'll get a ticket.  But your question is how much the fine..  I dunno,  maybe they throw it out, no fine, just court cost.  

I think it's the same in the UK technicaly illegal , but not always enforced. Most people here have a sat nav stuck to their windscreen, most people now have them tucked in the right hand corner so that they do not obstruct their vision. However the car can fail the MOT if anthing like this is stuck on the windscrean when the car goe's in for it's test. When the sat nav first came out they would be stuck anywhere some in the middle of the screens, there are some loopy people around here.