Explorer 36mm confusion

[Grin_and_tonic]

This is my first post on the board. I would like to purchase my first Rolex, and think the Explorer I 36mm is the way for me to go.

This watch has been around for a while, and there seem to be a number of iterations through which it has gone.

Is there any anything I should be aware of -- changes? / versions? / movements? / something? -- that I should aim for or alternatively avoid in making the right decision?

Also, what would be considered a "good deal" as price goes while still being in the realm of reasonability?

Thanks for the insight!