Splitting a network

Hi,

I'm working at an office that needs to split up their network for security purposes.  They're currently on a peer-to-peer network and only have two computers on it.  They would like to have a guest network for people that come in and want to use their wifi.  Also, their credit card merchant company says that they're not PCI compliant since the computer and credit card machine is not on it's own network.  They are on the same network that the computers are on.  Also, they're using their Century Link DSL modem (gateway) C1000A as their router--which I'm sure doesn't have the proper security that they need.  I was thinking about recommending a Sonicwall wifi router to them but I've had mixed experiences with the wifi Sonicwalls.  Can you recommend an affordable router solution for them to accomplish the split network, guest wifi and good security?  Please let me know if you need any further information.  Thanks for your help!