I added a bounty for 400r to this question last week and awarded it a few days ago:
Methods for improving color choice and combinations?
Today I was going to start another bounty to reward another answer. However, upon doing so I can only create a bounty for more than my first bounty. So, the only option I'm presented is 500r.
Why can't I add a 50r or 100r bounty now?
Is it just to prevent too much rep sharing?
(Which wouldn't really make sense since 500 > 100 :) )
This is done to prevent (potential) abuse. Unfortunately, you're not given the benefit of the doubt in this case and forced to increase your offer. Here's the explanation on MSE:
As noted by Robert, this has come up recently. Posting a bounty is a perfectly reasonably thing, a good thing (with badges too!). However, when applied repeatedly to a question it does start to represent abuse.
To help minimise this, but while leaving open the option of offering a subsequent bounty when you really, really are looking for another option we will be implementing a change here, where subsequent bounties have a higher minimum offering. This means you can't place 6 "cheap" bounties of 50 rep, to keep your answer on the bounty board to get lots of pass-by upvotes, as subsequent bounties probably1 will not cover your "spend".
We now double the minimum "spend" for successive bounties on the same question by the same user. So if you started at 50: your next bounty on that question has a minimum of 100, the next 200, the next 400, the next (max).
Another related change has been mentioned by Sam Saffron:
- If you are placing a bounty on a question you answered, your minimum spend is 100
1=Unless of course your answer is super-awesome, but if it is super-awesome it'll probably already be doing the rounds for free (insert obvious regex/html jape here).
