I rarely have tour clients who book rooms at the Best Western affiliated hotels in Paris. I think people are afraid it will be a generic chain hotel. But in fact the hotels are all independent. They are simply members of the Best Western marketing group that allows them (after passing certain standards, of course) to use the Best Western or Best Western Premier brand. Each one is completely different in style, atmosphere, size and of course location.
Some are recently renovated, stylish boutique hotels, some are rather old-fashioned and dated, but many of them are in the best neighborhoods in Paris and priced far below other hotels in the same area. Several located in the 6th district (around St-Germain-des-Prés and Luxembourg Gardens) are below €200/night, all of them are below €300. If you’ve got member points, you have a lot to choose from! If not, just keep in mind that you shouldn’t let the Best Western label scare you off, judge each hotel on its own merits (checking out the descriptions, photos, user reviews, etc). You may be happily surprised!