I was getting kind of tired of doing two separate baths for the big boys and the baby, but those baby bath seats are all $30 and up! I saw this one on Amazon, and thought, "That looks like a $40 glorified inner tube."
So I improvised.
$1 at Walmart last summer. It worked pretty well as long as someone was holding the tube for stability.
Later I found the baby boat I got on clearance at the end of the season a couple of summers ago, so he can sit in that pretty much unassisted. It is nice to plop all three boys in the bath where they are contained so I can clean the bathroom. They even do me the favor of dumping the water all over the floor so I have to mop...