A few years ago I bought two round beds at K-mart for only $15 each. I still have them- they are really durable, plus you can take out the inside and wash the outer part. The dogs (and cats) just love them and they've lasted a long time.

I also have a large "woolrich" brand bed from Target (they are around $40 for the extra large size) that Adele really likes. She always "fluffs" her beds and ends up ripping up cheaper beds, but I've had this one for a year and it's still in pretty good shape.

ETA: I just realized the Woolrich bed is in my signature. Seine is laying on her back on it.