Question about out of warrant repair and applecare.

Hi, a few months ago I bought an Apple Watch Series 5 and was dumb enough to not get applecare, and I broke it.

I would like know if I pay for the out of warrant repair, which is almost the price of a new watch, I would be able to sign applecare, or if the only way is to get a new watch.

Another question, my broken apple watch can be used as down payment in a new one or is just trash?