At the current price, not at all. Unfortunately the frenzy for the Eruptors has caused their price to be ridiculous. So the return just isn't there. On the other hand, if you can get your hands on one of Avalon's units or a fabled BFL unit the return is there. The Eruptors really only make sense if you are buying in large quantity. If it costs you more than $250 each there's no way you'll ever get the money back unless BTC makes a huge jump in the currency market. They really looked like they were going to become the mining unit of those without the funds for larger rigs, but so far the prices are too high to make it happen.
So it looks like the Avalon units are around $300 for 4.5 gh/s of hash power. Is this something that you think is feasible in terms of money and hash power?
Totally feasible, but the problem is availability. At this point, it's very risky to think you can get one on hand fast enough to make the return before difficulty jumps up. Those that bought them when they were running like $1500 are getting massive returns and if you could find one for such a price you would as well. The issue is that currently they are running more like $10k for a preorder and i see them going for $20-30k on eBay. At that price it's pretty risky even if you can get the thing in your hands and operating right now.
The main decider will be if the bottom drops out. If Avalon or by some stroke of the gods BFL actually starts getting their product out the door at a reasonable rate with stock on hand, the return is likely to drop out very quickly. Consider that there are barely any ASICs in play right now and the last difficulty jump was essentially one of the highest ever.