Bob - The least expense sextant is what some call a “lifeboat” sextant, which is plastic, and does not have a micrometer drum. Rather, you have to determine what the minutes are by where the correct hash mark lines up on the degree scale - a bit of a pain. A plastic sextant with a micrometer is easier to use.
The problem with plastic sextants is that the plastic expands when it comes out into the sun, and is not as accurate. But for training puposes it would be fine.
Here’s a good link to learn more about sextants:
If you have the time to shop around, there are all sorts of sources out there. I ended up purchasing a very good used sextant in like new condition from a pawn shop.