Hi Jim, here is the buck converter I got off of e bay. It was $7.95 each, but the more you buy the lower the price it looks like.
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Here are a couple of pictures of them in use. I use one for my 4.5v led buildings and I use some at 10v for other accessories. They are really easy to use, power in one the LEFT side and power out on the RIGHT side. there is a small screw right above the copper coil you see in the photo, and you use that to dial in the power you want going out.
I have 5-6 on my layout because I use a lot of old phone and tablet power sources to power my accessories, as I can get those for next to nothing or even free.
Just for precaution I would check it with a voltmeter before hooking anything up.