As tall as you are, there is no box-store bike that will fit you properly, and that is more important than weight or component quality. I opened this thread to add the comment that there are many decent box-stor bikes, as long as you get one without suspension and are willing to do regular maintenence. But most (all?) box-store bikes come in one adult size and it is to fit someone 5'6" to 5'10", give-or-take.
Your best bet will likely be an old 10-speed road bike... many of these were availalble in very lage frames (25" would be the minimum I would reccomend for you; I saw a 27" frame for sale on kijiji last night).
If you can find a mountain bike, 22" would be an absolute minimum size, but you would be better off on a 24" or so frame, although those are not common.
Edit: I am 6'5", and I have struggled time and time again to get comfortable on a too small bike, and tried swapping coponents and altering everything that could be altered... and have come to the realization that if you want to be comfortable you need a bike that is at least close to the right size.