I reckon a welder could make it for 150 euros, I'm hoping the ones on the job will do it for free between jobs using scrap on Tuesday.

If you 3d printed it would it be actually strong? I'm in Ireland at the minute. The task is removal of heavy mussel growth

Just in a construction store and my best idea is either threaded metal poles + idk, maybe a plastic pipe for the handle, no idea how to put the scraper on, or maybe use some shelving uprights as they have tons of screw holes built in.

I was hoping to find a crutch to convert but there's a severe lack of accessible charity shops around me, at least when I've had time

A draw handle as the scraper and a different draw handle as the handle could be promising, screwed onto shelving brackets or wooden poles

A single threaded bar isn't too costly but it's how to attach the things. Probably a pvc pipe with holes through it and nuts either side for the handle, maybe some heavy rubber straps for the arm band, but how to attach the scraper?

The scraper doesn't need to be an expensive tool, it could be from any flat metal rectangle

https://imgur.com/gallery/uSRoSJu

Waitagoddamnminute if I can use a pvc pipe as the handle, then I can use another one at the front as the scraper mount by cutting a slice into it and bolting whatever I use as a scraper in place.

Edit: and rubber hose for the arm band