Just saw these. Might be picking some up. I guess the C6220's are coming off lease so these are coming up. Sub $300 even with the bridge PCb. Two links:
Dell 10GbE Dual Port SFP Ethernet Network MEZZANINE TCK99 X53DF C6100 C6220 | eBay
Dell X53DF Dual Port 10GE MEZZANINE Card TCK99 C6100 C6220 | eBay
Dell 10GbE Dual Port SFP Ethernet Network MEZZANINE TCK99 X53DF C6100 C6220 | eBay
Dell X53DF Dual Port 10GE MEZZANINE Card TCK99 C6100 C6220 | eBay