Mine were freebies from work. They were a writing pen and a laser pointer combo. Worked great for me. The db meter, no need to get fancy. If your going to use a phone or something like that just use a stand so you're not part of the equation and use a painter tape reference on the floor with alignment marks for clocking the pickup mic the same direction the same time. I used a pair of Galaxy S3s that were both retired a long time ago. You could even pair them and WiFi the info back to a 3rd phone or laptop..
I'm frugal.. LOL Works sweet as can be.. Cost? 10 minutes of learning Doggle or VPN or Tethering or LOL what ever you want to use for FREE. You can just use one too. tape marks on the floor like I said..
Merry Christmas come to think of it..