Hi Scrappile. Like you I am starting intrasia and I just made my own. I took wheel oss slow speed grinder and bored to fit grinder shaft then turned blank approx 200mm
long to dia of inside of hot water pipe insulation foam offcut from a friendly plumber slid over blank ande made up sanding tube to fit over insulation .Am pleased how well it works. Would love a flex drum but cost $40 us.plus sand drums plus postage to NZ. plus exchange rate comes to nearly $100 NZ and log wait time. Only cost me about 1 hour to make I did put a grub screw through hardwood blank on to grinder shaft.