i have funds in bitfinex that i fund others with and it has been steadily increaseing. bitfinex is ending its usa customers so i am looking for another exchange. signed on to gdax and it looks as tho they do not have a place to fund
GDAX is part of coinbase, so you should buy your coins there.
Check Kraken, Bitstamp, C-CEX, Or maybe GEMINI to buy bitcoins, and see if they allow you to. They might have less competetive rates then bitfinex, but they work just fine.