I have two HRM:a Timex T5G941 and a Pro-Form Precision XT.
The Timex is simple - 3 buttons and one of those is the backlight. It keeps track of the average and maximum heart rate and the activity time. The Timex seems to get a strong signal from the chest strap and seems reliable. This was a gift a couple of years ago, so I'm not sure what the price was then. I think you could find one less than $40 now.
The Pro-Form Precision XT has many more features: chronograph, user info input, time in zone, time above zone, time below zone, activity time, calories burned, and more. The Precision XT HRM is not as reliable as the Timex. I wore it on a 45 mile ride and got a minimum HR of 0 BPM and a maximum of 220 BPM with an average of 142. Since I'm still alive, I don't think the 0 or 220 BPM were accurate. This HRT was sold as various brandslike Pro-Form, Reebok, and others. I paid $25 and shipping for it from someplace like Woot.
IMO, the Timex is a better HRM and the Precision XT is a better watch, but both are adequate for basic info to assure you're not over-reving the heart.