Further to yesterdays post about coprocessors. There is a blog regarding using FPGA's for computing and specifically integrating them into BOINC. Its called FPGA at home and can be found at http://www.fpgaathome.org/
In his post of 18th of July he links to an Xcell article in which they state that they used the XC6VLX240T with a MicroBlaze processor. Looking at the recommended pricing on the Xilinx web site for the board and processor it has them costing approx $2500.
I am not against using FPGA's for computing, in fact I think they should be used. If it can do maths when why wouldn't you use it? Its just that the makers seem to have priced them out of reach. Until they decide to get serious the likes of AMD/Intel will control the CPU market and ATI/Nvidia will have the GPU market to themselves.