Hook it all up into a rig that will consume <30 watts of power, so you can run it for pennies a day, and leave it on for a year. You might get lucky and make ROI.
The good thing about Block eruptors is that they take so little power, you can run them until the difficulty hits about 750 million, before they start consuming more power money then they produce. If you can set up a super power efficient rig, you may get lucky.
This is a small investment suggestiong, assuming you have ~200$ to burn, and are OK with maybe only making 100$ back. From my calculations, you can make ROI on block eruptors still, assuming you can run them for a year. the difficulty can't rise forever, it has to level off sometime, and I'm placing my bets that it will level off under 750 million at least until you can make ROI on the eruptors. Maybe next year, when the next gen ASICS hit the market, the difficulty will skyrocket too high.
And yes, you could just buy a few bitcoins and hold onto them, but that's boring If you want to get in as a hobby, go for a few eruptors and be content with only making half ROI (that's realistic, though I believe you'll make full ROI).
If you want to get into serious business mining, try to buy an early BFL preorder (back from late 2012) and hope that you get lucky on getting it delivered. Otherwise, pick a new company and hope you can get an early preorder. I've got an Xcrowd preorder in, I'm hoping I can get some good stuff going with that.
that sounds wishy washy super wishful thinking - you could buy those things...maybe...but thats money to burn...people thrive from high selling the block eruptors you will not find fair value outside of using groupbuys here ... instead buy gpus and do alts then resell those gpus later instead.