dave_the_m's Core Bug grant has run out and is up for discussion and extension. Through this first run, 159 tickets were looked at and closed, which are about 10% of all open bugs from when the grant work started. All of this was done on a grant of USD 20000.--, co-ordinated by the Perl Foundation.
With that number, we have a rough estimate how much at least a certain class of reported Perl bug costs to close. Of course, there are bug reports that are far easier to close, for example bugs without an attached test where more information from the reporter was requested and where the reporter has not answered since 5 or 10 years. Maybe these bugs are worth less than USD 125, but even if you can't or won't contribute money to TPF, or directly to a grant for core maintenance, going through the Perl 5 RT queue is a good way to help Perl.
An older discussion on the cost of Perl bug (reports) was done two years go by Nicholas Clark in spending other peoples' money. Nick also put some tentative value on various classes of bug reports and the work done on them:
$25 for correctly identifying* the change that introduced a bug or demonstrating that the bug has been present since 5.000 or explaining why it is not a bug, and should be closed $25 for a committed TODO test* or for identifying the existing TODO test [may well be cheaper to write a new test. I don't have a problem with this] or for identifying which bug this is a duplicate of, and me +rging it [bugs in dual life modules can't earn any more, at this point*] $50 for Perl code that is committed to blead that fixes the bug $100 for Bourn shell, Makefile or other code that is committed to bl +ead that fixes the bug $150 for XS or C code that is committed to blead that fixes the bug $200 bonus for fixing bugs present in perl 5.000 $400 bonus for fixing bugs present in perl 1.000
The "bounty hunt" proposes a value of USD 150 for each bug of the kind that Dave Mitchell fixed. Without looking at the actual types of the bugs fixed, according to this scheme, Dave Mitchell would have received USD at least USD 12475 out of the hypothetical bounty pool, and likely some of the bugs would qualify for the 5.000 bonus or at least come close.
Looking at the numbers, it seems to me that the cost/value proposed by Nicholas is at least in the same ballpark, even if it is not consistent on the level of five minutes of research into the bugs and individual time spent on them. So maybe these numbers actually are representative of the actual cost of a bug (report).
There remains the problem of supply and demand. There are only few people with the knowledge required for some Perl internals, so it is unlikely that all reported Perl bugs can be closed by simply plopping down USD 150000.-- to close 1000 bugs (plus some money for communications/management).