I’m in the same situation. I was looking at regular scaffolding at Home Depot that is listed for $143.
Then I found sections on FB and CL for around $100. I’m actually picking up 2 sections tomorrow.
my local john deere dealer has a tractor they rent out (not sure which model but it's got 30+hp and it 4x4) with a loader and choice of backhoe, york rake or brush hog for $275 per day. when I do my garage next year I think that's the route I'm taking.
No matter what you do your garage will NEVER be big enough. So, make make it as big as you can (legally and financially) and just talk to your neighbor and let him know what you're going to do but like mentioned above some landscaping might make things easier for them to swallow.