However, this is still too much work for me (I'm lazy). I don't want to have to enter the date - my phone already knows the date, why can't it do it? I only need a few categories, and I don't want to have to type them in. This sounds like the perfect place for Textexpander. If you're unfamiliar with Textexpander, it essentially allows you to create system-wide text macros. So, if you're sick of typing in your address, you can assign a text trigger, such as ".address", and every time you type that it'll insert your address. The macros you make on the Mac can sync (via Dropbox) with your iOS device, which can come in very handy.
Textexpander got even more useful a while back when they added fill-in snippets. They describe fill in snippets like this:
You can add fill-in fields to a snippet to make it easy to create customized boilerplate text at the time you expand an abbreviation.
I made a fill in snippet to automatically enter today's date, a blank field to enter a payee, a list of expense types (software, advertising, hardware), and a blank to enter an amount. I set the trigger to be ".exp", for "expense".
It looks like this, if you're interested:
%m/%d/%y, %filltext:name=payee%, %fillpopup:name=type:default=software:advertising:hardware: %, $%filltext:name=amount%
So, I open Drafts, type ".exp", and it immediately takes me to the Textexpander fill-in. The date is already there, I type in my payee, select the type, and enter in an amount. I hit Done and return to Drafts. I hit the EyeDock Expense Dropbox action and I'm done.