It depends on really how much you're going to use it and how much you're going to smoke at once. Remember, it's low and slow. A full packer brisket can take 18-24 hours to be "done". Ribs, anywhere from 3-9 hours. Pork shoulder/butt 6-12 hours.
I have several homemade models that I had welded using new, clean 55 gallon drums, and 2 bullet type water smokers.
A bullet or WSM is very easy to use and a good choice for beginners. It looks like a short squat rocket. There's a fire pan on the bottom, a drip pan on the next level, then 2 cooking surfaces. It can hold a decent amount of meat, and is easy to regulate the temperature. A full pan of coals will last up to 6 hours. And they're relatively cheap.
Intermediate models run between 250-600 bucks. They're better built, with thicker walls, have a larger, separate cooking chamber, and a separate smoke box.
Then you have the higher end models, that run from about 1,000 bucks to whatever you can con your wife into thinking is necessary!!!
But you can get great results with just a drum, some rebar, and two heavy bowls. I would start with a bullet, as they're nearly put together for you, it takes about 10 minutes to put it together. And they're pretty reasonably priced. You'll get years out of it. I'm going on year 8 with my two bullets, and barring the smoked up paint job, they're good as new.