Is mom sticking to her guns on this or does she now regret her actions?
If mom understands what she has done, then start checking out Craig's List etc. and when you find one, present her with the bill. Maybe she'll pay it. At least she may understand what she has done. Here's a lead.
http://mobile.craigslist.org/bik/1330231734.html.
$100 for the bike, about $120 for shipping.
Here's one for $250
http://chicago.craigslist.org/chc/bik/1334869607.html
and here's one at $450
http://portland.craigslist.org/mlt/bik/1332988468.html
And when you move out, take everything valuable to you WITH YOU. Mom sounds like she acts before she thinks or talks.