TI 5518/5152K 8 channel Equibit EVM board - $100
I'm not sure how much interest there is in the Equibit stuff at this point, but this is a really cool EVM board. The 5518 is an 8-channel modulator, and includes on-chip routing/mixing of inputs as well as per-channel biquad filters. The 5152 is an 8-channel power chip providing ~80W of usable output or so per channel. This board actually has 2 of the channels paralleld for use as a sub/lfe channel so it's aimed at a 6.1 setup, but the biquads mean you can do a full 3.1 active xover setup right on the board.
This includes PC software to set up and program the board. Once programmed it will remember the settings so it can be used standalone. You have to enter the biquad coefficients explicitly rather than specifying '3rd order butterworth', but 'glt' used to have some code in his blog to help with this process. I'm not sure whether it's still online though. I had my own code to do filters - I'll see if I can dig it up.
Info on the board is still available on the TI site here
TAS5518-5152K8 Evaluation Module (EVM) - TAS5518-5152K8EVM - TI Tool Folder
Asking $100 plus shipping, but open to offers. I may be able to get this into a USPS flat-rate box which will make shipping cheap, but would also open it up to international customers.