I know what you mean, and I'm torn. This project was built in about 4-5 hours on a Saturday, mainly as a chance to learn about mail handling. It's ugly as hell and there are no tests (!), so I don't know how well it will hold up as a long-term solution - I guess we'll see.
I just find the $9/month per employee a bit repugnant - if we grow to 10 people, we'll be paying over $1000 a year for a piece of software that parses subjects out of emails and stores attachments. Doesn't seem like a good deal.
As a rough guide, you might factor in another 8-10 hours, because, according to Fred Brooks, a proper programming "product" takes about x3 as long as a "program".
Taking a wider view, there's an appeal to "cloud components", where all components are rented - including ones as simple/trivial as this. For this to work, it has to be cheap enough to be a no-brainer (esp for projects made of such components). Say, 1/100 - pennies - e.g. 9 cents /m/e. In the long-term, you'll see free open source alternatives, and maybe even free hosting (cloud providers supply it free, to support their hosting of your actual app)... and maintained.
I will give you the answer now -- it won't hold up :). Parsing and handling email is notoriously finicky, and every app I've written or maintained to do it has a constant stream of little bugs and edge cases that must be tested and handled that grow over time.
Would be interested to see a followup in 6-12 months.
Instead of simply looking at the absolute value of the cost per employee, compare it to the time lost to the current method of accounting. Do you lose $9/month in work per employee on expense processing?
If it takes employees an average of 5 minutes per month, you don't have a problem. If it takes them 2 hours per month, investing $9/employee/month is a net win.
Hosting your own on Heroku isn't cheap either. Not to mention even more time savings when you go the paid route (interfaces into accounting software and what not).
I just find the $9/month per employee a bit repugnant - if we grow to 10 people, we'll be paying over $1000 a year for a piece of software that parses subjects out of emails and stores attachments. Doesn't seem like a good deal.