You can buy floorpans from other venders that also includes the seat supports already welded on for cheaper.
Stoddard for example, you can buy the left and right pieces, with the seat supports already welded on, for 400 total.
Click to view attachmentRestoration design, you can buy the front and rear pans, and seat supports for $518.
Click to view attachmentI've also installed both front/rear pans as well as L/R side pans and I would say the only advantage to using front/rear pans is that you can get a cleaner seam since most of the weld area is flat.