Just waking up your canister every second is work, actually a lot of work. It is not heartbeat that is charging more, but try sending your canister 1 message every block, not cheap either!
For more flexible scheduling, you could use something like IC Cron. I’m not sure if @senior.joinu (author of IC Cron) is offering a deployed IC Cron canister as a public service for everyone. But as a community, if enough people find it useful, you can collectively fund such a public service (e.g. using tip jar) in an open and transparent way that benefits everyone.