I forgot to add, another cheap and simple background is the sky. look on my Website at my Cymbidium images, and you'll see some which I have photographed against the sky to show them at their best.
You have to put the plant on a stand that enables you to get lower than the plant and photograph it upwards, again preferably using the tele lens to frame the plant to what you want to see.
http://www.users.on.net/~op_ink/AD/C...m_Orchids.html
And this one
http://www.users.on.net/~op_ink/AD/Oncidium_Orchid.html
to see what I described above using a single color background with the plant forward of it and using the tele to eliminated shadows.
ALL these images were shot on an Olympus 6 Megapixel point n shoot camera!