L.P.
I've had an au pair for four and half years now. I've had a different au pair each year, and while they were all different, they all added great insight and experiences with my 3 girls.
I joined because my oldest daughter has special needs, and needed someone to help drive to appointments, etc. What I found was that all the kids benefited from individual attention, not being in a crowded after school program with little supervision, and in the case of my youngest, she could still go to preschool - but only part time, as now she goes to dance or gymnastics, the park, zoo and other adventures with the au pair.
I use Cultural Care, but there are other good agencies (I just think mine is the best...) My au pairs have been from Poland, Finland, Sweden, Germany and now Sweden again. I stick with European girls as they seem to be the best drivers, but some friends have a Mexican au pair who is also really good.
I haven't had the issues with the girls not wanting to do the work, but I'm pretty up front about what the week will look like, what use of the car they will have - and they tell me after they arrive, there were no suprises.
Cost savings are nice, but be prepared to do your homework up front - and to spend a lot of hours thinking about how to integrate, working with au pair, bringing her to get her drivers license, etc. I found that I didn't do it until I was a year in - but when I spent the time, it made it way easier for the others who came after my first, Marta.. :-) I'm lucky she was so patient with us...
Good luck to you!