I'm not sure that this has anything to do with web apps, or even necessarily perl at all.

It's a very general question: you're being paid to do something. Someone else is doing the paying. That someone else is expecting to reap a return on their investment, whether that is by, in turn, reselling the fruits of your labour (an employer or supercontractor, "super" being merely the opposite of "sub", not a statement of superpowers ;->), or it is by improved sales for reduced cost or improvements in internal processes to lower costs, or to penetrate a new market, in your case, via the web (when you sell directly to a customer).

For example, I participate in the development of off-the-shelf software. Software is so cute in this way: the price actually paid by the customer is a factor of what they get out of it, and has little bearing on what I am being paid, since the physical costs are so low (CD, box, manuals). I don't worry that my employer makes millions (USD) on a single sale, while paying me a tiny fraction of that (in CDN). My personal rate is based on my skill set, and my personal productivity and value to my employer. How much work can I accomplish, in how little time, helps determine my pay rate. (Also, how much money I could command in the market should I decide to check that out - this is a factor with my employer.)

How much is your time worth? Whatever the market will bear. As a student without a formal degree, I would think that $15-20 USD per hour is reasonable. Any more than that, and people would expect you to have things accomplished faster and more reliably. Any less than that, and you're cheating yourself. Remember that you get what you pay for - that applies to your customers as well.

That said, if you only make $1-2K, I have to think you're a heck of a lot more productive than we're giving you credit for, and should charge more money ;-) 100 hours at $15/hr is $1500 - so you're thinking this will take 2-3 weeks of full time work? You must be better at this stuff than I am, and I make significantly more than $20USD/hr ;-) (to be fair, my job has nothing to do with web apps.) You'll chew up 15-20 hours just in talking about what needs to be done, nevermind the actual coding. And be sure you're being paid to talk as well as code.