Honestly I wouldn't expect much. It's not an insignificant amount of work to get something packaged up and shipped out, especially if someone isn't in the habit of shipping already. Frag the coral, adhere it to a plug, let it heal up for a few days, prep the package, bag the coral, package it, tape it up, weigh it for postage, create a label, and take it down to the shipper. It's a lot more work to do that than it is to just trim back an overgrown coral and toss the excess in the garbage. Some people would be willing to do all that for nothing but goodwill, but most people will want some compensation for their work.
Additionally, I think you underestimate how much shipping actually costs. Most of the online coral vendors get price breaks because of their volumes, and on top of that they'll usually eat a portion of those costs in the hopes that the profits from your order will cover what they eat. For a regular person to ship overnight, you can expect shipping costs to be $40-$50. The only 'affordable' overnight option is USPS Priority, but it's not a guaranteed service and can often take 2-3 days to arrive; sometimes corals can survive that, but not always, and I wouldn't count on it from someone who's just throwing something in a box for free.
You'll have far more luck trying to snag freebies if you find local reefers and simply pick the corals up from them - it eliminates most of the hassle, especially if you can bring your own bags.
Alternately,
@uniquecorals is also in Cali, and they have some of the most reasonable shipping costs in the business. I wouldn't say they have a massive selection of low-cost corals, but there's still a decent amount if you just want some life in your tank. $25 for regular overnight shipping and just $150 for free shipping. Pick up 5 $30 corals and you'll have a pretty good start for a good pico tank.
