A perfect probe can easily cost upwards of $100, but it will be money well spent. There are so many different probe thermometers on the market that they can confuse you. Not all have to cost a great deal to be suitable, but it depends on what you need. Ideally, you should get one with a digital readout. Here you will leave the probe in the meat while it is cooking. When meat cooks to the target temperature, the probe thermometer will sound.
Certain aspects may not seem important, but they are. You need to check the battery life of the probe and the size of the monitor. You do not want to get mid-way through the BBQ and find that the battery has failed. If you want to show green credentials, a probe with rechargeable batteries will be a good choice.