It seems almost all commenters here are agreeing with the premise that ‘posters [have] to crosspost to both’.
I don’t think this is true. It leads to people subscribed to both having two identical posts with different responses in their feed, which is annoying. Just post to the one that you’re ‘closest’ to, or pick one at random.
Part of beauty of federation is that you can see all the content from multiple places. Cross-posting is not required!
"Jinos 3D Filament” is pretty cheap. I started using them during the pandemic when it was hard to find PETG. Seem to be a small place in North Carolina that manufactures mostly for their own use? Sometimes they take a couple of days to ship.
They sell mostly on eBay: https://www.ebay.com/itm/382556327412
[Edit: Just re-read that you’re looking for ABS/ASA - I don’t think Jinos does those, unfortunately]