Where to buy one and what should I expect to pay? What features to look for and stay away from. Thanks

A $50 one from Home depot will get you close.

I bought a JR Overseas about 25 years ago. I Like it and is still working currently. I paid 300 way back then on special pricing during a boat week in Florida. It was money well spent.

I bought a $30 General pin type a few years ago and have used it many times for transom repair and just for wood. What are you wanting it for?

transom checking. I have an older Formula. I didn't want the pin type because I thought you had to penetrate the wood, and I did not want little holes in my gel coat. I was looking at the scan type but was not sure if they are accurate.?

Do it from the inside rather than the outside of boat.

If this is your boat take a 1/4 drill bit and start just above the drain plug, go in about 1/2 inch. If the wood comes out dark and wet and not blond and dry you have water intrusion. Can repeat this further up if needed. Seal with 3M 4200 if all good.

I was rebuilding mine so was removing glass and used it as I went along