Here's something like what I do at work. Syntax not quite correct, I'm sure. It's a C++ project, but you can probably adapt it to your situation. Making the TAGS file takes a while every now and then, so you might want to run it as a cron job.

shell:

   find rootdir1 rootdir2 ... rootdirN ".*\.[ch][ch]?" | etags > /convenient/dir/TAGS

.emacs:

   (visit-tags-table "/convenient/dir/TAGS")

need a class or function in emacs:

   (tags-apropos _regexp_)