Ok currently a very small network I know

Simply a 4 port DSE router connected directly to my PC thru CAT5
however I recently moved into a flat with a girl who has a laptop, she suddenly would like to pay for half of the braodband, providing she can access my router wirelessly. 802.11b/g

Is my best option to

A) Buy a new wireless router.

B)Attempt to add in a wireless access point ( bout 50-60 dollars )

The security would be simple WPA passkey stuff and perhaps simply MAC address blocking. ( or alllowing )

Whats the smarter option.