As for heart monitors, I've seen Polar recommended the most and are pretty reasonable. You have the option to get a watch just a hart rate monitor or one with a gps as well. In addition, you can either do a hand-held one where you dismount, or you can do one that measures the heartrate as you ride. Of course, depending on what you select the price increases, but I think the wrist watch eith only the heart monitor plus the handheld device you take their pulse with is at or even under $100.
I, personally, picked up a sprague stethoscope (as in for people) for $17 from Norco and dismount, pop the stethoscope behind his elbow, count the beats for 10 seconds, then multiply by 6. I'm volunteering at my first ride this month, so I'll have a better idea of how the vet checks go, but you can also use the stethoscope to check the gut sounds. Once I start conditioning for 50's, I'll want a little more specific and real-time info about my boy's vitals as I ride and will probably invest in a Polar model, but for now the stethoscope is great and I'm learning a lot more about maintaining his health!
A note on stethoscopes - don't get the cheapest ones, but don't bother getting one more than about $30. After you go beyond that mark, you'd have to spend over $100 for any real difference in quality, and that really isn't necessary for what we need them for.