Check out www.avionics-laf.com if you need just the boxes.
Same ballpark when it comes to advertised prices for Avidyne: www.airwerkscfl.com
Sarasota Avionics has currently an upgrade/trade-in promotion for 430/430W/540/530W. Trade-in value seems reasonable, but the base price is 2k higher.
I would buy all avionics from one source and preferably through the installer just to avoid any discussions and finger pointing in the case of a malfunction about of the root source.
It’s my understanding Avidyne & Bendix King did this due to Bendix Kings larger presence around the world, with the thought if would open up new markets for the IFD. I found out about it a couple years ago and found a great price on a rebranded IFD440, so I bought it
In the BT peddler talk, Eric is selling 3 of the BK rebranded IFD 440's NIB. According to him (and he knows avionics), they are supported/updated by Avidyne but just have a different bezel. I think he was at 12K each. If I hadn't already bought my 750xi, I would be tempted to go that way.