Well, it's been a while and I needed to dig a pile of receipts for all of my vintage motorcycle hobby..
Tubing & flat stock $100
trailer tire, hub, spindle $40
CrMo rod ends etc. $200
pillow blcok bearings $40?
used GL1100 air shock $40?
welding/machining (labor) $355
total $775'ish (not including the price of sidecar itself)
I think it's much easier to build a new leaner frame than modifying conventional non-leaner sidecar frame.
Typically rigid sidecar shocks got strong springs to reduce rolling. I guess you can use it for leaner but the ride will be harsher but then again it depends on the passenger. Mine is a skinny 9-year old so I picked up regular motorcycle shock.
If you carry adult passenger, then maybe you should lower the center of gravity. Mine is for child only and I mounted the sidecar body high so that he can look around (I think his eye height is about the same as or a bit higher than sitting in a passenger automobile.)
Rear mount: Uses two U-clamps on motorcycle frame
Front mount: Uses two U-clamps on motorcycle frame
Sidecar suspension (old version):
Note: Initially I put the sidecar wheel in the middle between motorcycle front/rear tires to support the load better. This turned out to be a bad idea. People say for the leaner, sidecar wheel should be on the same axis as motorcycle rear wheel. This is to eliminate sidecar wheel's influence on motorcycle steering.