Thanks for the wafernet link. Let me check this out.

Actually, I have costed most of the embedded TCP/IP projects. Most cost less than 30$.

I have also checked up the SN2000 network card based design. This uses a readily available network card.

Tthe best and cheapest option would be 8052 + realtek/cirrus chip. Royalty free tcp/ip Protocol stack is available from Atmel and others. Some projects atop at frame level. Re-assembling frames and porting to RS232 will have to be tried out. But, again, if RS-232 to Ethernet becomes or is available within 30$, then it wouldn't be wise to build it.

Thanks again