I'm fairly certain you're aware of this, but...
Two options here: flat rate or hourly. Both are easy to compute.
Flat rate = number of hours (minutes) spent on document x your suggested hourly rate.
Hourly rate = start at the minimum amount of money you're willing to work for.
Freelance rates vary wildly. A fair medium (which I use) is nothing less than $25 an hour, and for specialized gigs, such as the Ivy League shit, is $40 an hour. However, I will state my price at $50 an hour to dissuade them. I don't want to write entrance essays, but I will, for the right price. Currently, both of my steady freelance gigs are at or around my minimum; one gig is super easy, flat-rate work which comes out to roughly $20. If it wasn't insanely simple work (for me), I wouldn't do it.
There are a lot of freelance gigs out there in the $10-15 range, particularly on the research based sites like Wonder. They're offering $28 flat rate for some shit that's gonna take at least two hours.
Sounds to me like you put in a bunch of effort. You would not be asking too much for a flat rate US$100 (TWD$3300) - I would ask for $250, unless it was a friend or family. I dunno how many hours you put into it though. The last one I did was about 10 hours of bullshit (same as you described, but not Ivy League). And that's...$25 per hour.