Return on Investment Question

Hi, I recently started playing the lowest limit multi table tourneys at pokerstars 45 seater $1+.20.

My aim is to play 500 tourneys without going broke off a $50 initial starting investment.

After 79 tourneys I've made about $43 profit with a ROI of about 46%. I know this is chump change to most people but I want to be sure of myself before I move up the limits.

My question is this what sort of ROI should I be aiming for over my 500 tourney target. Is 50% a good figure to shoot for or should I be aiming higher or perhaps lower.

A little guidance from those more experienced would be welcomed.

BTW I've just read Harrington on Holdem and it's excellent would highly recommend.

All the best

Koy