Howdy from Texas. My name is Chris, and I have been a part of the motorcycle community for many years. As I approach my 66th birthday next month, I find myself more excited than ever about my riding adventures. I currently ride a 2005 Honda Goldwing that I bought new, but I've decided to add a sidecar to my collection. The Goldwing, as you can imagine, is not getting any lighter, and my wife thinks she might ride again with one. I'm open to any advice or recommendations, as this new addition is not just an inexpensive new toy, and I would like to budget around $ 10,000 for it. From what I've seen, it might be easier to buy a complete rig and sell mine. I attended a Ural demo day to ensure I liked riding with a sidecar and, indeed, I loved it.
You've done a very good thing in this process. Going out on a trial ride in a rig is a great way to determine if you have a brain storm or some other brain event.... 
You will get several recommendations to your question about build a new rig or buy one with a GL1800 tug. My recommendation is to buy an existing rig with Hannigan, Champion, DMC (Texas) or other heavy, reputable sidecar builders (assuming you want to stay with an 1800 Wing as a tug). If you're open to other bikes as the tug, there's a lot of options out there.
A build will be in the neighborhood of the $10k you describe, possibly a bit less, but transportation to and from the builder will be some additional cost. My suggestion is to call Texas Sidecar in Teague, Texas and have a conversation with them about options. They won't steer you wrong. Phone: (254) 218-3990
Glad to have you in the wacky family!
Illegitemi non carborundum est!
@thane-lewis Thanks, Thane. I will call TSC and have a chat. They are only a couple of hours from Dallas. If I do go the complete rig route, I do think I will stay with a Goldwing. I saw a rig with a 2018 GW somewhere, if I recall correctly. 🙂
