Lots of DIY options out there (I have an Ugly Drum Smoker, aka UDS), but if looking to purchase commercial, the entry point for a quality smoker is definitely the Weber Smokey Mountain which is a fantastic cooker and reasonably priced.
The WSMs are also quite easy to sell should you decide to move onto the something fancier. Not that you necessarily need too, lots of competition cooks win with WSM and UDS.
I am perfectly content with my UDS, but my wife thinks it is too ugly (imagine that), so she wants me to get a Big Green Egg next year to replace it and my aging gas grill.