You may be able to get decent results without resorting to mod_perl, depending on what your site does. I co-run a plain-perl/MySQL website with over 200,000 users pulling data from a (growing) 1.5 million row table. We're talking about 30,000-40,000 database hits per day and the site runs with almost no delay most of the time. Neither the database nor the code is very complicated, and the data that's accessed is very small (about 100 bytes per access) but it's survived 300% growth without any noticeable degradation in speed in this environment.
in reply to What if mod_perl is not an option?
Of course, we didn't know that when we started, and our ISP has mod_perl available in case it ever becomes an issue. Bottom line is you may not need mod_perl for what you're doing, so if you can't easily change ISP's you might still be ok.