anyone suggest a 'cheap' b-roll camera to 'match' my z5?

not looking for any bells and whistles - just a cheap, clean picture - sound unimportant.

tia

How cheap? There are an array of less expensive matching cams in Sony's CX lines. The ones with the larger sensors match pretty well and often can be run in auto mode. I've been using a pair of CX550 (about 1/3" sensor) in multi-cam shoots with an NX5 and FX1000. The current versions 1/3-inch sensor cams are (I think) the CX 700 and 560. (The 560 is viewscreen only and has a smaller -- 5 hour -- recording capacity). The less expensive CX cams have smaller ¼ inch sensors and lesser controls and lesser recording capacity.

Take a look at Panasonic's TM line of 1/3" 3-chip cameras. The 60p is very nice and at a decent data rate for AVCHD. The camera has a ring that can be focus, zoom or iris. There's a shoe and a mic input that is handy in a pinch where your wireless receiver can be used. Whatever camera you look at, pay attention to the datarate. You will want to grade it to match your Z5 and the more data, the better it will suffer in post.

Obviously the best match would be a used FX1000. But if that's over your budget, I'd have to agree that a used cx560 or 700 would be a good choice. But be aware that you will need a smokin' fast PC to handle the mixed formats on your timeline, even if you shoot 1440 AVCHD rather than 1920.

You could always pickup a A1 or V1 or Z1 on ebay.