I bought the next step up in the tripod as it had the larger diameter legs and is rated at 80lbs+ so a bit of overkill involved. Just a little bit over your budget. Different brand same tripod
Although I picked up a nice gimbal a week or two later. The gimbal is so much smoother than a ball but it is bulkier and heavier as well so a tradeoff.
Nightsnipe is a great choice IMO for a ball head/tripod. For under 400, the hunter elite combo has been a solid performer for me. The head itself holds the big bore steady as a rock via pic adapter. Added a BOG grip for other rifles. Smooth locking knobs and not bad weight wise to lug around. Removable leg for bipod use too.
I forgot to say anything about the Bogpod Death Grip Carbon Fiber tripod it looks pretty nice too and has a universal clamp up top as well. Plenty of people using these so they must be OK.
I would be thrifty and purchase cheaper tripod legs if you don't have to carry it to far and go with the Slik legs linked below for $100. They are really solid legs for $100!
I would splurge on the head. You will never regret it. The Really Right Stuff Bh-55 Soar is an awesome shooting and photography head. I love mine! I have it combined with a carbon Gitzo tripod. The Anvil 30 is another popular choice but less versatile in my opinion.
This combo costs about twice what you are looking to spend. However, it is absolutely worth saving your $$$ for and doing it right the first time. If you don't like the head you will be a able to sell it easily for little loss of money. RRS heads are very desirable on the used market.