I get the idea of instances, like you can make your own and this is good for privacy. But some lemmy instances are much more popular and this in fact makes it another Reddit. If there are separate instances for niche topics, why not make it another community inside a larger instance?
Well you can get a domain with a weird TLD for $2-5 a year and $40-80 once for a SBC like a raspberry pi to run it. Ideally you’d want a small 32-64gb ~$20 SSD or HDD for storage, but in a pinch a USB stick or micro SD card that you can get for ~$5 would do. Any old computer can handle it though, Lemmy is pretty lightweight, you would have resources left over on the host to run other services. So in total if you wind up in over $100 something went wrong somewhere.