Go wireless SLF....
I've had a 2/3 machine network in the home office for 5 years and went ADSL (sharing the connection) a year ago. The main drawback with connection sharing in this manner is that the host machine must always be on (and working). Since my setup is so old I am going wireless now that the new standard is out.
If you are not already using broadband, that part of the cost would be there anyway. The wireless network seems to be no more expensive than the wired if you want an ADSL router - trust me, you do. It gives each machine independant access to the net and to each other and to peripherals attached to both.
You need - wireless card for each machine, ADSL modem/router and a broadband line with filter.
It will be very flexible - you can shift PCs without problems; visitors with wireless laptops will have access to your LAN.