Depends on where you live.
check out this Australian site its the cheepest i could find and if you
spend more than $55AU postage is free.
Plants:

http://www.aquaria.com.au/db/shoppin...reshwater&Cate
gory=Plants+%2d+Live


For everything else you cant go past:

http://www.aquaticlifeaquariums.com....t_67.html&lang
=en-gb