I recently upgraded my venerable old Forerunner, (made by Garmin) for a model that included a HRM. I think the cost was about $150 on Amazon. Since I needed to replace my aging Forerunner (which it seems I can't run without these days) the little bit extra for the HRM was worth the price.
I only use it periodically, but when I do I have been very pleased with the results. Garmin, is one of the leaders in the GPS industry and I have had super luck with them, including a replacement for my orginal Forerunner when it crapped out even though it was long past warrentee.
2.5 years, 45 pounds later... 128ish pounds