Huge fan of anything with the Powermatic 80. Mine gains about 3 seconds per day. I wear a Rado but I believe both Tissot and Hamilton also offer this movement.

Go for the second hand speedmaster from a reputable seller. This is the one you want and will eventually buy. If you really want to know more than you should about the watch, get the moonwatch only book. This is the bible that will help you to check everything from every version ever of the myth. Even if you don’t buy at the end, if you’re a geek I can assure you you’ll dig the content. The movements in those Tissot watches are crap, you’d be better get a serviced vintage in the 500-700 euros range than those glorified fashion watches in my opinion.

Good starting points for first Swiss mechanical are Tissot, Hamilton, Mido, or Certina. They all belong to the same conglomerate (the Swatch Group).

The "gateway drug" these days seems to be Tissot PRX. Their quartz models are about half the price of their mechanical ones.