You may have to abandon all self-respect, though. See
this story at macrumors.com about the "iFart Mobile" app, a fart noises toy which was at that time the biggest-selling app. Sales figures per day, with ranking:
12/14 - 841 units - #76 overall
12/15 - 1510 units - #39 overall
12/16 - 1797 units - #22 overall
12/17 - 2836 units - #15 overall
12/18 - 3086 units - #10 overall
12/19 - 3117 units - #9 overall
12/20 - 5497 units, - #4 overall
He's since revealed to us the most recent sales numbers for the last couple of days which includes the coveted #1 spot on the App Store's Top 100 sales.
12/21 - 9760 units, #2 overall
12/22 - 13274 units, #1 overall
After Apple's 30% cut, that means the iFart Mobile is generated $9198 in one day.
It's depressing to think, but in some ways he hit on the perfect app: needs hardly any development, and has very broad appeal (everybody farts, and a fart is the same in every language, so no difficult localisation is needed).
You don't need huge sales to cover the cost of becoming a registered developer. The value of your time is something only you can judge, but I'd say that the experience you gain will be worth it, and if you succeed in publishing some apps this could help you land a programming job later, even if they don't sell well.
Disclaimer: I haven't done any iPhone development myself. These days (outside my job) I only program to "scratch an itch", and so far my needs have been met by existing apps. I don't have time to write a program which does what 20 other programs do already.