You are awful at math. Based on your earlier statements about having to drive to meet people, etc it would seem that by month three you would be netting a lot less than $8 an hour using your model. And to buy 7500 worth if $50 phones you would need to acquire and sell 150 phones, or about 5 per day. If each requires an hour if your time from start (locating, buying) to finish (sell, ship, connect money) then you are commiting to 30 hour work weeks for less money then you make now.
So good job on that.
$50 is just the barometer. I've bought phones anywhere from $200 to $300 dollars. I bought my ex-girlfriend an iPhone 4S Refurbished for $300 off some schmuck and sold it $450.
The deals are all out there. All I had to do in this particular example was click a few buttons and be in the right place at the right time. You can literally make $50 - 100 off certain cell phones.
Throw in bundles, repairs, etc. And it's actually all quite profitable. And there's no price on being your own boss.