I'm the kind of person that definitely works better if I know I'm working toward something specific. When I first joined mturk, I calculated that as long as I could make only $2.50 a day, everyday, that would be enough to cover the cost of my student loans and still have $10 left over monthly for small luxeries. However, I've been on mturk for a few days now and I'm noticing that, on average, I'm making $7-$8 per day at the minimum. So, I've been rethinking my goal. Not sure if I should aim for something 100% doable like average $5 per day just in case I want to take a few days off or if I should push myself to try to make $9 or more per day. Either way, I'm pretty happy so far.
You sound like you really fit in here. If you have at least 1000 hits, try for $15. Put a little bit away each week for a rainy day.