If you wanted something active, check out the Mi-Si acoustic trio, which is rechargeable (no batteries).
Or if you want to run on batteries and have tone/volume control, the Shadow nanoflex for Ukuleles is an economic + good choice.
There is a cheapo Mahalo active pickup for ukes too.
While it's a good deal for a cheap pickup, it's nowhere as good (or reliable) as the ones above. You gotta ask yourself whether it's worth making holes in your uke for such a cheap pickup.