Not cheap - I paid 13k for mine, because it'll be delivered sooner than anything ordered now, which is 10k
However, if you research this (also use forum.kncminer.com) you may come to the same conclusion as the rest of us:
The future of bitcoin is unknown, and the factors which dictate possible ROI are, of course, ever changing.
Difficulty, bitcoin price, network hash rate. These are the metrics of concern. Use bitcoin profitability calcs to give you an idea of how this speculative investment might end up.
Its very speculative, but I think that lots of us who bought tickets and are riding this crazy ride believe Bitcoin value will continue to increase which will result in profit. Naysayers will believe bitcoin will either crash completely and be worth nothing, or they believe that the difficutly of mining will quickly out pace these machines and render them to nothing but expensive heaters.
However, you can't be sure... good luck whatever you decide to do and hopefully nobody is spending their mortgage payment to buy an ASIC super computer.
https://www.kncminer.com/products/neptune-second-batchEdit: maybe some persuasion is in order. I urge you to please research what your proposed hash rate will "earn" you (mined coins - cost = Profit). I must say that very few rigs can be profitable, now. Please don't take my word for it because it's only my opinion based on the information I've gathered. You may come to another conclusion. However, I would hope you'd research this point very seriously before "investing" any money.