Try Bittrex, Poloniex, Kraken, Huobi.com, and Kucoin.
I suggest that you use coinbase or bitstamp to buy bitcoin
With Bitcoin you can transfer it to Binance, which is the most reliable cryptocurrency x cryptocurrency exchange (they don't receive USD deposits).
Then you will exchange BTC for any cheap alternative coin you like.
Binance will
no longer serve US customers, starting on 12 Sept.