Depends on what BB's you'll need a tool for. Some bb's use a totally different tool than others. Some
use a similar tool, but slightly different size. Buy some socks or gloves while you are there.

If you are only going to use it a few times, you might be better off just taking it to a LBS. If you are regular customer of theirs, they'll probably do it for little to nothing.

I've got a BB tool and a few others tools I've only used once because the cranks I replaced the old with required a different BB and therefore needed a different tool.