Choosing TCP/UDP ip core (+ mac?), no SoC, anyone?

Here is a link to a low-cost TCP-UDP core: http://comblock.com/com5402soft.html

The core is written for Xilinx devices, but should not be to difficult to port.

A pure UDP transmitter isn't that difficult to write yourself. There is a UDP Offload example on the Altera Wiki: http://www.alterawiki.com/wiki/nios_ii_udp_offload_example (http://www.alterawiki.com/wiki/nios_ii_udp_offload_example) You can remove the NIOS part.