Doing Paris on the Cheap...
Not sure how frugal she is, but I've had some great experiences staying at hostels in Paris. Check Rick Steve's "Europe Through the Back Door" on Paris. I've stayed in a lovely converted building from the 14th century. Mornings we were served endless cafe au lait and baguettes. It's also a great way to meet people. Hostels tend to be very "open" to meeting fellow travelers...And the hostel experience is not just for 18 year olds. It's a very popular thing to do in Europe and I've met everyone from nuns to nuclear partical physicsts at hostels. (Really!)
When I backpacked through Europe, I joined a hospitality exchange organization. Believe it or not, people welcome other travelers in their homes (travel vicariously, I suppose.) SERVAS is a popular organization, but there are many others. I stayed with an attorney for the EU in Brussels, with a lovely family in Paris with a beautiful flat, Amsterdam with a couple who owned a B&B, a student in Berlin, etc.
Here in the US, I've hosted a guy on tour with Cirgue du Soliel and an East-Indian swammi on his way to a retreat in Canada.
Hospitality exchange is a great way to see a city through a local's eyes...and forge many great memories. I've gained much more out of the experience than a free night's stay....