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haha... BTC isn't even divisible down to that (yet) so I suppose it's 0.00BTC per day. Not sure if he was trolling with that eBay post or not, however, if he wasn't, I'd say save your money and put it towards something that will help you out later in life, like for college/an apartment/car/whatever. Many of us got into this as a hobby, expecting to make our money back in a year or so (if ever)... It wasn't really until November that profits from mining could actually become a "job"... The problem is the cost of entry is already quite high if you want to make anything worthwhile. A standard 4 card rig pushing 2500Kh/s is only making around $20-22 a day after power costs, and costs $1600+ to build with the scarcity of GPUs these days. In order to make $100 a day, you are looking at around $8000 minimum... and that's assuming you have the circuits available, a way to cool the space, know how to build and configure the computers, etc... Once you get much beyond 20MH or so, you start to need a dedicated power panel, even better cooling, switches to network everything together, redundant power arrays... now you're talking over $20,000 easy.
When i started i didnt invest too much but i was lucky, had a pc laying there un used managed to snatch a gpu on cyber monday cheap... took till last week to make ROI back (from december) just purchased gpu #2 i still see this as a hobby that happens to pay for its own electricity and leaves me some change, i do like messing with the settings and tweaking my pc its a nice hobby but not in it to be rich.