Hello there!

[Phantom]

Hi there Nic.
We can always use good wranglers and support staff. If your kids have costumes they can sign up for the Galactic Academy http://www.galactic-academy.net/

If you are looking for a cheapish costume there are always Imperial Officers, Imperial Crewman, Reserve Tie Pilots. There are soft costumes and are relatively cheap compared to hard armour like storm troopers.
http://databank.501st.com/databank/Costu...icer_black
http://databank.501st.com/databank/Costu...ridge_crew
http://databank.501st.com/databank/Costu...erve_pilot

Or just have a browse through all the costumes:
http://databank.501st.com/databank/Costuming:CRLbyname

Have a read over this thread to give you an indication on the membership process:
http://www.501st.com.au/forum/showthread.php?tid=6720

I hope this helps.

Enjoy and remember to ask loads of questions, stay clear of ebay.