I have $500-600,
For the money, you can't beat the Weber Smokey Mountain (WSM) 22". If that was my budget, that is the unit I would buy. It also depends on how much food you want to be able to cook at one time. If it isn't that much, you can find a used "Good One" smoker on craigslist. I used to have the Open Range model and I loved it. Awesome for butts and ribs.
For big cooks I like my reverse flow stick burner, or gravity feed Superior, but for home cooks, even up to 6 or so butts I have to say the old uds does quite the job, no complaints here, you can build for under a $100 or you can buy a nice one already made for less than $300
I agree Danny, but he said he had a budget of $500-600, for the money one of the best stickburners on the market, but even used you can't find one that cheep, wish you could I would have another one good luck fowldarr