Junkyards are fun .. Sometimes it's worth the challenge to find something used or cheap and make it work. Never would want to skimp on safety stuff , but if its a newer battery and holds a charge , $30 seems like a good deal to me ! Probably will find some other neat stuff there while looking around too ... If not , you can still by a new one
BTW.. I'd be a bit ashamed of myself to let some parts store guy "install" my battery.
Good luck with the hunt