You can get a 3 or 4 pack of plastic drinking tumblers (short, wide cups) at walmart, kroger, most grocery stores, and the majority of them will float just like the log, and they're usually about a dollar for a pack. :) I don't cut the bottoms off, and my guys just go in, hang out, and swim back out when they're ready. Works just like the betta log, but so SOO much cheaper. :)
They're food and dishwasher safe, so they're completely safe for betta, no worries about chemicals or anything like that.
And, they come in all sorts of colors, which is nice. :)