The Freescale MCF51CN128CLK ColdFire V1e Microcontroller costs $6.79 in single quantities. The CLK variant comes in an 80-pin PQFP package, and includes a 10/100 Ethernet PHY. This is easily hand-solderable given sufficient skill. Freescale provides a support package which allows FreeRTOS to run atop the 50MHz core, with the open-source LWIP TCP stack as an optional module.
There's also a decent fact sheet available from Freescale