I used to wash my brushes and dry them upside down on my towel bar, but after moving I no longer have towel bars in my main bathroom so I needed a new way to dry my brushes. I decided to get one of the small Benjabelle Brush Tree's off of Beautylish.
This small one is the Daisy model and it's $19.95. I got white, as they were sold out of black and I was too impatient to wait for the black. The two piece base snaps in and out of the top, it's three pieces total. The idea is you can take it apart to store it, you can also store it put together if you have room. It's plastic with silicone like holes for the brushes. You just push the brush handle up from the bottom after washing and it lets them dry as they should, upside down.
I got the small one as I'm never washing all of my brushes at once, usually just a few. So the size of tree will just depend on preference for you. It's a fantastic little tool and works great. I would recommend one especially if you don't have a towel bar.
This is how I used to dry my brushes with elastics and a towel bar:
