If it was possible to "just buy a rig" and if I had the money I would do it.
I even thought of placing a few FPGA miners at our company because electricity is basically free (well, at least i do not have to pay for it) and I have control of the IT. But those miners are hard to get and a little bit expensive.
If you don't pay for power and you have money, buy some decent rigs and do it. Biggest problem is where to get rigs from lol
GPU mining may be an option but I think it is more difficult to setup a decent Hashrate compared to FPGA or ASIC.
Try mining LTC and convert them to BTC maybe? Whatever. I tried using like 5 or 6 PCs/server from our company for mining but that is really a waste of energy. Forget old GPUs, forget single GPUs, forget CPUs.
To get a hashrate which can pay your expenses in a short period of time you have to have really fast devices..late miners are basically fucked. "The [mining] world is yours" was valid before the block reward was split in half and when difficulty was low.
I really envy people who mined a few thousand coins and did not sell them until this year. Lucky bastards