Not exactly a "cheap" tuner, but many of the better effects units or personal practice tools have built in tuners capable of tuning 5 and 6 string basses.
I have a Korg PX3B Pandora that does a very good job of tuning my basses.
My TASCAM CDBT-1 Bass Trainer also has a built in tuner, and so does my Zoom 506 pedal.
Off the three, the Pandora tuner is easier to use and correlates better with my rack mounted tuners (both rack tuners are also Korg)
Peace,
James