That's because you're using Bitcoin, for which custom ASICs are a thousand times more power efficient than commodity hardware and so commodity hardware is useless, but custom ASICs are stupid expensive.

What you want is a cryptocurrency that ASICs are no better at than CPUs or GPUs, so can use an ordinary CPU or GPU that will pay for itself more quickly because most of the mining cost is electricity instead of hardware. (Hint: the hardware you want in this case has the best performance/$, not necessarily the best performance/watt.)