... there even is a Mark 3 Sextant by Davis
Actually it is a training sextant, but a nice intrument to start with at only about 60 USD and if you can live with the possibility to end up some more miles off your true position because it does not have the worm adjustment with a vernier scale with a reading to 0,2 minutes, that bringst the accuracy down to 0,1 natical mile. Thoretically, and only at a dead calm sea.
So, under more realistic conditions I found the results I got with the MARK 3 not too bad...
An if it comes to the decision to invest in a high end model, the Mark 3 makes a perfect spare stowed away in a locker that does not need any attention as all metal sextants need to keep them from corroding...