Those that feel bitcoins and ethereum are too expensive should look into litecoins. They trade at 27 a coin. Also ripple just came off a nice run to become very relevant in the crypto currency game.
Even GBTC has a ways to go. It's tied to bitcoin and bitcoin will likely hit $3500/4000 by December(its pushing $2100 tonight). That puts GBTC at $350-400/ share by December.