The first thing is to find out what size is right for you. Soprano, concert, tenor or baritone. Many people start with the concert size. If possible try out some instruments to see which suits you best.
James Hill suggests that you start with the size that allows you to hold the uke in the crook of your arm and your fingers naturally reach the fret board between the top edge of the body and the sound hole.
There are lots of decent ukuleles to be had for around $50. They will sound and play reasonably well and will allow you to decide if you want to continue. Any cheaper than that and most likely you won't like the way it sounds and it will be difficult to play chords and strum. If you can spend a little more, do so. But don't go crazy.
Enya, Flight, Makala also offer inexpensive starter ukuleles that are pretty good. Do some research with online reviews of different brands and models.
I second the ukulele club route. You'll find friendly people and you can hear various instruments. Some even have beginner ukes at the meetings for you to try. Stores can be a bit overwhelming with so many instruments. It's much easier if you have watched some videos and read some reviews and know what to look for. Knowing a little of the lingo helps when you talk to a person at a store.
Get a tuner. Some places will give you one if you buy a uke from them, or one may be included in the box.
Most important: Have fun looking. Ask questions and keep an open mind.