I bought some water kefir grains on ebay a couple months ago and could not be happier with the result.
The package got stuck in customs so it took 10 days for it to arrive. I thought for sure they would be dead but they have done nothing but produce delicious water kefir and propagate. The kefir tastes like a bubbly lemonade/ginger ale and I find myself craving it now. My friends and husband who don't really like kombucha do like the water kefir. Most recipes suggest using raisins, but I couldn't find any unsulfured so I have been using prunes or dried apricots. Tasty, seriously!
I also bought some milk kefir grains and I am not as thrilled with them . . . maybe I'm just not used to the taste/texture or how long to culture the milk kefir. I have been putting it in smoothies and using as a base to make salad dressing. My husband has been drinking it plain a little, but not me! The grains themselves are growing plump and seem very healthy - they were also in the 10-day delayed package and survived.
I think that while $20 sounds steep, it's probably worth it since it's practically free to make kefir and you want to get a strong, healthy strain. Mine were about $30 for a group of one kombucha mother, about 2 tbs water kefir grains, about 2 tbs ginger beer plant (very similar to water kefir) and about 1 tbs of milk kefir grains.