Here is a cheap way to make your own multi-flash set-up that I put together from simple parts gotten at any hardware store.
Aluminum Stock 3/4" x 4' around $5
Aluminum Stock 1/2" x 4' around $5
12 thumb-screws $3.00
16 washers $2.00
4 wing nuts $1.00
Will make two adapters
Total: $8.00 per adapter with extra aluminum to make a couple more
I use a Giotto Mini-ball $13 as the base swivel for the whole adapter.
The cold shoe adapters... I had some lying around but you can get them cheap.
All the parts you will need. Simply but some aluminum stock and cut it into sections, drill out three holes on the base and three with two bends for the umbrella adapter. Exact dimensions aren't critical... you could just eyeball it.
Double flash set up with umbrella mount... ooooohhhh look at the cool lights shining on it! :D
Here is a shot of the pieces set to be put together for a quad flash set up. Notice the high tech rubber band... fancy.
Four flash set-up.
Umbrella inserted into the mount... and the rubberband creates the tension to hold the umbrella in.
Four flashes with no umbrella.
Four flashes with umbrella mount... swivel at base allows for rotating and aiming of the light.
So there you have it... a cheap easy way to make your own set-up. Let me know how it works for you.