If noise isn't an issue, you could buy 3 x Antminer S9s for about $6000, inc. PSU (+ shipping + duty). The S9 runs at a little over 1.3kW, so around 4kW for 3 of them. Combined, they should earn approximately 100mBTC (0.1BTC) per month (a little under $1000 at the current exchange rate), not counting electricity costs.
The Antminers s9s are very loud though, they're a riskier investment and they only mine one algorithm (SHA256). Unlike graphics cards which will likely retain some retail value, if the S9 becomes unprofitable to mine with, it could become practically worthless. Having said that, it would take a much more powerful/efficient ASIC miner (and a lot of them) to have a significant impact on the global SHA256 hashing power, which is already huge.
Something else to consider: As a business, you should be able to class some of the mining hardware purchases as a investment expense or stock. In the latter case, you could probably claim stock depreciation from a tax point of view. Any electricity used is a business running expense and what you earn through mining does not become liable for tax until you either spend it or convert it into fiat (that's the present situation in the UK at least, although taxing cryptocurrencies directly is pretty much an impossible task due to their anonymous nature).
