Feature-wise nothing even comes close to PowerGREP, so the question is, how many compromises are you willing to make? I agree that PowerGREP's price tag is a bit steep (not that I have ever regretted a single penny I spent on it), so perhaps something cheaper might do?
UltraEdit is an excellent text editor with very good regex support. It supports Perl-style regular expressions, and you can do find/replace operations in multiple (optionally pre-filtered) files with it. I'd say it can do everything you want to do according to your question.

RegexBuddy, apart from being the best regex editor/debugger on the market, also has a limited GREP functionality, allowing search/replace in (pre-filtered) subdirectories. It's also not free, but considerably less expensive than PowerGREP, and its regex engine has all the features you could ask for (the current version even introduced recursive regexes, and the extremely useful ability to translate regexes between flavors). Big pluses here are the ability to do a non-desctructive preview for all operations, and to have backups automatically be created of all files that are modified during a grep.
