I am a full-time nanny so I wanted to reply to your question.
Nannies get paid anywhere from $10 - $18/ hr. Some nannies are salaried at 40, 45 or 50 hour work weeks and many get $400 - $700/ week.
Younger nannies without experience might work for $8-$10/ hr.
If you only have one child and only want the nanny to do typical activities (with no extra chores) $10-$12/ hr. is common. Many nannies are asked to do the grocery shopping, cooking, light cleaning, errands, etc and then they can expect to be paid more.
Some common benefits for a full-time nanny are 2 weeks paid vacation, reimbursement for miles driven in their car during work hours, $ towards health insurance ($100 is average).
If you can't afford these things, try to think of unique benifits you could offer. My employer lets me park in their heated garage (some families make you park on the street!), use of internet while baby is sleeping, leave early one night a week to go to school, etc.
I hope that helps. Please feel free to contact me if you have any questions.