USB miners is like the dumbest decision you'll ever make... They profit you literally nothing, especially with the difficulty rising quickly.
So you buy a stick from sidehack or a reseller cost in the USA 30-40 dollars.
Just 1 your point it at this pool
https://bitcointalk.org/index.php?topic=1283990.0if we hit a block you get .24- .25 btc
if you are running a pc 24/7 the extra power is 5 watts about 4 kwatts a month about 50 kwatts a year.
at 12 cents a kwatt 6 dollars so for 1 year maybe 45 dollars and 2 years 51 dollars.
the chances are we will hit a block if we play for 2 years.
I plan on running mine for year's most likely. I might sell a compac or two to pay for electricity eventually. But as of now I'm just enjoying using them.
And I think the long term Phil mentioned really is important. Talking about year's of running not just a week or two. We stand much better odd's then some think by running for so long.