To do this one right you will be in it for several hundred dollars. Yes, you can do one cheaper. I'm in the process of scripting out a plan to build one...locating a food grade barrel can be a challenge to some. Also, I have a couple of contacts for welding but I will have to send it out to a local shop for the paint job.
I own a Weber for grilling...smoking on it takes a bit of time learn. Make sure you by the larger diameter Weber.
Have had two made for me in the past. I came up hwy 43 from Mobile and saw several efforts wasting away outdoors. They managed burning the lids and gave up I suppose. But the right hardware, hinges is all important for the lid to close properly. And try to find some 3/4" stainless steel diamond wire for your rack. It will be your highest expense and will last the life of your grill w/o fear of rust and it's far better than any alternative. Get a large sheet of the cheap stuff (square pattern) to cut into about four pieces (extras) for the bottom grate to keep the extreme heat from the body.
The best crafted drumstyle grills (I've ever seen) are at Carmeuse. a limestone plant in Saginaw near Alabaster, AL and the guy who works there wants $275-325. He generally totes a couple around in his pick-up truck to show off AND YEAH, HE'S THAT GOOD. You can't get a manufactured one close to this w/o sacrificing space. Have never spoken to him only inquired through a friend that pulls a deluxe trailer grill that he uses for events.