Since you use $, I think we're an ocean apart, so I can't give you some. But def ask around at your local organic produce store, or pin a message wherever hippies / health nuts / counterculture people hang out.
Fermentation
Would bottled water kefir be a suitable starter the way unpasteurized bottled kombucha can?
Maybe. I've never had success that way tho.
No but I got tibicos on Amazon from a company called Gut Punch and they perked right up and worked great. They were not expensive. I see some in the $12 range now (mine were about $8) and remember you only need a teaspoon or so, they multiply like tribbles.
Where are you located? I know a company in France who gives away their surplus grains, you just need to pay for shipping.
I am in Utah, near the capital city. I have found one company that sells bottles of water kefir and kombucha that said they would sell me starter kefir grains for 5 USD. I would just have to pick it up at their head quarters.
Seems like a decent deal.
Definitely better than what I am seeing online.