Chuck (B/Rs) beat me to it. Wanting to buy "a trapdoor" is like going to Baskin and Robbins. We'll need to know more of the what & why before making a lot of recommendations, other than the basics:

(1) Don't be in a hurry - they (except for a few models which would not be a good choice for a novice anyhow) are NOT rare.

(2) Get to know what "old" is supposed to look like. Avoid ANY sort of refinishing like the plague, unless you just want a cheap shooter with no resale value.

(3) Do some homework so that you know what piece goes with which model. There are a lot of mix-masters out there.

(4) Spend some time browsing   (You need to Login. Feel free to ask our opinion of any auction on which you might be interested in bidding.

(5) Don't become one of those guys who say "I just bought a xxxxxxxxxx for $$$$, how did I do?" That is one of the world's dumbest questions - if you do not already KNOW the answer, your wallet should have stayed in your pants pocket!

The search will be exciting.