You might consider a Novotel Inn. My wife and I have 2 teenage sons with normal teen-age appetites so we attempt to pay the least combined amount for lodging and a big breakfast that will last a long time. We usually find that sleeping 4 in a room saves money. We stayed in a Novotel in London in 2007 and were pleased with the simple clean comfort, professional and courteous staff, and proximity to a London Underground station. It offered an English-style (i.e., big) breakfast for all of us. We arrived early on our first day and Novotel has a room where travelers can leave luggage until check-in time. Another plus was the variety of nationalities who were also hotel guests.
We are going to London and Paris in April 2009 and we determined that the Novotel Paris Les Halles is located in a central location convenient to Gard du Nord, a Metro station, and the other sites at the top of our list. Another factor was that, at the time we made our trip plans, Novotel was offering discounts for early booking http://www.novotel.com/gb/hotel-deals/index.shtml.
We tried something that you might consider. We created our own personal Paris map on Google Maps (if you haven't done this before, try it because it so simple that we learned how to do the first time). We placed markers on our Paris "hot spots" and placed markers at potential hotels. On a second computer screen we brought up a Paris Metro map showing the location of stations and the direction of the Metro lines. Having those two items simultaneously available visually helped us identify several hotels that were located more central to our desired spots.