+1 on Leisestrum's advice and welcome.
It's not hard to spend 10K on a tandem. From your post I don't know the extent of your experiences with Tandems, nor did I pick up on that if you went for the lower cost opportunity, would it prevent you from pursuing a custom tandem in a year or two?
I would recommend writing down what you and your partner like about your current bike, what you don't like, and what you want to gain in a new bike and share that list here. It will help frame what you are looking for and it will also likely spur comments such as "have you considered...", or "I thought that and it turned out differently..." You get the drift.
At the end of the day it's not how much you spend, it's do you have the right bike for your team and are happy with it.