Ahh okay. I wasn't including the price of the dev kit, just the modules themselves.
If you want to go for the cheapest startup route then you can use an AVR microprocessor, ISA NIC like the RTL8019, AVR GCC for the compiler and uIP for the TCP/IP stack. The programming cable is reasonably easy to make or you can buy them for about $50.

If all this sounds a hassle then you can buy the boards from EDTP. There is source code on there as well which will help you interface the NIC chip to the microcontroller.

I've been looking into this stuff recently as I'm designing an ethernet gateway for a company. It's using a Cypress PSoC CPU however so it's a bit of squeeze on RAM.