> 50$ bills are frowned on in retail

Where would that be? On every trip to the US I have exchanged cash, EUR to USD, resulting in mostly $100 bills which I've used everywhere, sometimes even for rather small purchases, and there's been no frown upon that (after few purchases I also get my hands on smaller bills which are also more convenient).

Maybe it depends on where you are making your purchases, but I've rarely seen a $50 bill unwelcome at retail in Michigan, Pennsylvania, New Jersey, or the office park neighbourhoods of California.