I have Heartfelt but I know a lot of brothers on here use Michael's/ Shailala beads. You have to look at it this way, it's a one time expense, there stable and no mold. You could spend 90-150 dollars for an oasis or similar device and it quit in a year or so and have to start all over again. Also if you search the threads about cooler/ vino s I think you might be able to get by with fewer beads than you think, but you can never have to many.
Just my
PS. before you ask or someone else suggests it, stay away from kitty litter.