We did not have one for DD and it was fine. We had a swing and a bouncy seat and a moses basket. I think that the bumbo has a shorter "life span" than those because you can't stick a newborn in a bumbo.
That said they are great for some babies- I watch a 6 month old who isn't mobile yet and borrowed one from a friend and it's great to put him in so he can "watch" his brother and my DD play.
Do you have any friends w/ toddlers or even 9/10 month olds who might be able to loan you one?
It's definitely one of those items I would borrow over buy.