Looking for an reasonably priced matte box to use 4x4 circular polarizer--any suggestion?

Cavision has a 4x4 clamp-on for $250 and a 4x5.65 clamp-on for $400.
Matte box details at Cavision Matte Boxes (http://www.cavision.com/Mattbox/Mattebox.htm)
Pricing at Cavision Enterprises Ltd. - Matte Boxes (http://cavision.biz/matteboxes.aspx)

Thanks Mike.

I'm currently using a century wide angle adapter on the stock canon lens, it's 105mm, I see the Cavision fits 120mm, can that still be used?

Sorry Mike but I have no idea.
I looked into this line at a convention several years ago and was impressed with the quality but never ended up buying anything due to budget restraints.
Email them and ask them.
As I recall, they used to be very good about getting back to users who had questions.

I use the Red Star DV DSLR Pro II Matte Box Complete Bundle w/ 15mm Swing-away Arm, Top French Flags & Side Wings, Rubber Donut, Filter Stage and Filter Tray. Has 2 4x4 rectancular filter slots. It states its for a DSLR but it works perfect on my HM750

Recently got a Vocas (Century) MB-250/255 used for around $500. I like it because it's considerably lighter than many of the "cinematic" options out there, but still has two stages for 4x4s and two really neat internal eyebrows for controlling light. A little spendy new, but there are a few on eBay now and then. The MB-250 is a 105mm and there is an adapter ring for the newer 114mm MB-255.

Matte box MB-255 | Vocas Systems (http://www.vocas.com/products/mb-255)

I just bought the same one (Vocus) and love it over my Century Optics Matte box for its dual stage filter holder. Its MUCH much lighter than the OCONNOR on my AF100 which is very heavy.

Mw