That lens is a beast. Honestly, I have been really satisfied with the Manfrotto 290 Xtra Aluminum Tripod with Ball Head for my backyard birds. It works well for that heavy weight and usually stays under your $200 budget. No complaints about stability tho, it doesnt tip over even at 600mm... its a solid way to save cash while getting the job done.

Honestly you should check out the Neewer 66 inch Carbon Fiber Camera Tripod Monopod. It is seriously amazing for the price! I love how it handles my heavy setup without feeling like it is gonna tip. Ngl carbon fiber is a lifesaver when you are moving around the yard too. For under $130, its a total bargain and keeps those bird shots super crisp... definitely a game changer!

Nice, didn't know that

Be careful with cheap heads because that Sigma has a lot of torque. If the locking mechanism is weak, the lens might just flop forward and smash your glass. I nearly broke my gear when a huge lizard ran across my boots while I was shooting... those Florida iguanas are getting out of control lately, honestly they dont even care about people anymore. Anyway, just make sure you check those weight ratings tho.

been thinking about your weight issue for a few hours now. i remember when i first got my long lens and tried using an old kit tripod i had lying around... total disaster. it was rated for plenty of weight on paper but the moment i tilted it up to catch a hawk in a tree, the whole thing started to creep down slowly. i ended up super satisfied with my current setup only after i spent a weekend measuring the exact center of gravity with the lens hood fully extended. honestly, finding that specific balance point is way more important than just looking at the max load capacity. i actually had to mess with the mounting plate position for ages because the torque was just too much for the locking collar to handle comfortably. no complaints now tho, it stays exactly where i point it. quick question before i get into specific specs... what camera body are you actually mounting that sigma on? if you have a heavy pro body or a battery grip attached, it completely changes how the weight sits on the tripod head. also, are you usually sitting in a blind or standing up while you watch your birds? it really affects what kind of height stability you are gonna need.