If you would like an Ethernet solution and cost is an issue, have a look at using the low cost ENC28J60 chip. This doesn't have as much of the TCP/IP stack as the WIZnet ethernet shields, but you can get a shield that does UDP or TCP networking for less than $20 one off . The enc28j60 chip is around $2.50 in 100 off quantities so you may be able to negotiate a good price on 100 boards.
http://www.nuelectronics.com/estore/index.php?main_page=product_info&products_id=4