@Cr8tive Leo
It looks cool, have you thought about using 4 AAA batteries? I have been using 4 AAA NiMH 1000mAh batteries straight into my USB devices/hub with a small filtering circuit and it works perfectly.
At 5.28 volts under load it is well within 6% variation and should drop slowly until fully drained at about 4.8 volts, once again well within 6% variation.
Being NiMH they should handle any number of devices without moving parts and likely even would run a 2.5" hard drive, possibly with a capacitor to aid in spin-up.
I bought a super-slim USB 4-port hub made by Sakar at Staples today, they are on close-out and cost about $8.
I used a 4-cell AAA holder with a power switch from Radio Shack to power the USB device/HUB and used a motherboard USB Female cable removed from the bracket for a socket, came out nicely I think

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I used a prototyping board and some resistors from Radio Shack for the circuit, if I knew how to solder surface mount devices I would use a tiny tiny USB host termination IC under the Samsung e810 shell on the EXT plug
(I was the guy who pioneered the Samsung e810 serial mod on the Forums and Wiki

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So far I have only tested it with moving data back and forth from my brothers Creative MuVo, my Kingston Datatraveler and my other brothers USB SD Reader. I even copied from the USB SD Reader to my Kingston DataTraveler, it takes a bit of time on USB 1.1, but any Divx video file should play back just fine, and the PSX ISO's load in a flash from my Western Digital 80GB external 3.5" drive

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Edit: Omars, even if you only asked for an estimate you should realize that it is incredibly difficult to give one, I would judge it to be worth well over a $100 easily if you wanted the fair-market value against the GPH BoB and the hand-assembly.
He did snap at you, maybe he had a bad day or something, but he did explain why an estimate wouldn't be possible, you could investigate building a similar device yourself.
I personally want my USB to be across the back at the top next to the SD slot, and fit 2 AAA batteries per side in a "Sega Game Gear" style, I think that would be the best in terms of reliability, of course I couldn't have a keyboard that way

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