You'd have to be very lucky to find a Dreamcast cheaper than an A500, but it's a good excuse to get an excellent console with an awesome catalogue of games. It's the console that I have by far the most games for and I generally like the games more than those for the other consoles (I do have all of them, but the Dreamcast is absolutely my favourite).
You can find a nice deal on new Dreamcasts
here. I'd recommend going for the hardcore pack which has a couple of excellent games - including the very first game to be developed using a free SDK and KallistiOS.
Regarding floppies.. well, you'd put .adf files on there and play them, so think of it like an Amiga 500 jukebox.
