I would recommend a new buster for a Deneb. Then you could use Zorro III DMA mode and 100-BaseT ethernet.
However USB could eat a lot of system resources, what CPU & RAM do you have?
The cheapest solution would be a second hand Hydra Systems Amiganet Zorro II v1.0/v1.1 card and an AUI transceiver. People avoid them because they have no 10-BaseT connector but the AUI adapters are dirt cheap. Bonus is that no Buster upgrade is required.
http://amiga.resource.cx/exp/amiganet2000
