As far as the value...from what I understand it is basically based on the rewards pool. The initial number is just an estimate. Most likely, the actual final amount will be less (though I have seen it go up).

The money is distributed via the Rewards Pool. Basically a certain, fixed amount of Steem is created everyday to be doled out as rewards. Based on all the posts that get upvotes, and the weight behind each upvote (and downvotes), it distributes the Steem accordingly as either Steem Power or SBD (Steem Blockchain Dollars). So if, on the day of your payout, there were a ton of big upvotes to lots of posts, the value across the board will go down. If there was less distribution than expected that day, it might go up. It's hard to predict.

As far as the actual amount that YOU receive, it get's broken up between 1)Beneficiaries, 2)Curators, and 3)Authors. You are the author of your post. But if you post on DTube or Busy, they might have beneficiary rules in place that allow them to take a percentage of the payout from posts that are created (or actions taken) on their platform. This is how they make money to pay for devs and encourage people to develop new platforms on Steem. The max beneficiary percentage is 25%. Then Curators (people who upvote your post) could earn up to 25% of the rewards as well, depending on when you upvote and they upvote.

The rest goes to the author as either 100% Steem Power or a 50/50 split between SP and SBD. The SP gets calculated at a 3 day average price of Steem to the USD. So, If your payout is $10, and the average price of Steem was $5, then you will receive 2 SP. SBD is where there's a weird situation. For that, it's a 1 to 1 payout. So for that same $10 payout, if you did a 50/50 split, you would receive 5 SBD, and only 1 SP. Since SBD might be worth $5 too, you actually make more money this way at the moment. Originally SBD was meant to be pegged to $1 USD. But it's now way more valuable.

So ya, not complicated at all....