Like others mentioned, we need more information to comment intelligently.

What code(s) are you getting?

Is your transmission having shifting or slipping issues?

I wouldn't pay a shop for anything just yet until you do the appropriate research first to confirm a transmission replacement is actually necessary.

If you are truly in need of a transmission swap, I would not go the used route nor would I allow a shop to rebuild it. Your best bet is to buy a remanufactured one from Toyota. Remanufactured means all the moving parts are replaced. You're basically getting a new transmission other than the housing and other non-moving parts that are reused.

I will also echo what @octanejunkie suggested by buying from Joe Joe via Facebook. He will get you the lowest price for a Toyota Remanufactured Transmission. He's totally legit. Thousands of guys order from him and I've never seen a negative comment regarding his parts service he provides to the Toyota community. Here's a link to his page: Facebook Send him a personal message and tell hm what you need. He gets back to people fairly quickly.

For the swap, you can use my video series to tackle it yourself and save big time in labor costs.