Expect to pay for experience. If you're hiring an adult with plenty of experience with kids, especially someone who is not a friend or relative, be prepared to pay a competitive salary. And by competitive, I mean comprabable to what the nanny/temp daycare services would charge.
You will have more leeway with a teenager..but not much. Most if not all teens have a wealth of work experience under their belts, and are accoustomed to a real hourly salary. With that said, there will probably be few who will be happy with a flat $5 like kids from the old days.
Just remember, teens today have to pay for everything from cell phones, car and the car's upkeep, school books and supplies, college savings and more. While alot of that stuff was considered a luxury a while back, today, these things are necessessity for many young people and they'll probably be less inclined to do a babysitting job for anything less than minimum wage.
For both adults and teens these days, daycare is full of serious responsibilities and liabilities that most would feel need to be properly and fairly compensated.
The only babysitters I know that will happily accept 10 to 20 dollars for a whole night are very young sitters (as young as 11 to about before driving age at 15) just starting out. They have less bargaining chips and are more likely to settle on a small salary. But once again, there are more risks for you in this scenario, even with so many kids today going through "Babysitting Training" programs through their local community ed programs or Girl Scouts.