Cheapest

What Would Be The Easiest, Cheapest Way For Me To Measure Stress Levels For My Science Experiment?

Stress causes the brain to siganl the release of stress hormones, one of which being adrenaline/epinephrine. Adrenaline increases heart rate as part of the ‘fight or flight’ responce to stress. Would the easiest and cheapest way for me to measure stress be to measure heart rate? What device would i need? Where would i get the device, how much would it cost, etc.?
Thank you!

Subliminal MP3s Powerful Subliminal Messages