No there's no limit.
In practice the maximum reached so far is nowhere near 30,000 though.
At the time I answered the question here (with DataExplorer data from November) there were 25 answers across the SE network that had been awarded bounties in excess of 1,000 reputation.
Overall the highest was an answer on the Tex site to How to extract each pair of two adjacent cells of a table into a separate tight page? (+2050). Tex also has another 4 answers with +2000 bounties.
As Ixrec points out in the comments this has since been overtaken by some margin by Story where the number 3 is the monster? on the SciFi site - currently at +3,100.
The highest on StackOverflow is Improve GeSHi syntax highlighting for T-SQLImprove GeSHi syntax highlighting for T-SQL (+2000).