There's a 30-sheet Automatic Document Feeder for copying, faxing
or scanning. Can't remember whether it was $399 or $299 (bought at
Harvey Norman), but there's a $100 rebate in the form of a cash
card
Might be quite useful for you :D
If you need help, for combining and merging, I can do it at my
office with very very little hassle. I don't need to claim any
credit for it. All I need to do is to put all the pdfs into this
specific folder, then have a file that directs the server to
combine all according to the filenames I put up, and voila, it's
done!
Only thing is... I dunno how to use the office scanner, if not I
can let it auto-scan even faster :D => I guess 1 paper
will only take like.... few mins?
And an evil suggestion:
With regards to the bandwidth, whether you lock it a not, people
can still download and use up your bandwidth. Perhaps you should
implement it in such a way that people will need to key in a
password before downloading. The implementation via javascript
using a .js file shouldn't be that hard, and this should stop most
amateurs; not everyone knows how to download and sieve through
everything to find the password. For those that manage to get the
password, after all their efforts, they will still find that they
need to have the password for the pdf 
I think I'll do away with the password when I am free. PDF
conversion is not a technical problem. It is just an unavoidable
hassle to optimise the documents after combining. and visually
check that the scans are ok and pdf after optimising is ok.
Yah, the Xerox PE-220 seems to be really cheap at $399 before
hopefully a still valid $100 cashcard rebate and I will look into
acquring one provided it can do duplex.