Where do I put my switch for maximum effect

So I have my network broke into 3 zones.

Zone 1 is my Internet demarc to router (cable modem to asus 66u)
Zone 2 is my LAN community (including cabled and wifi)
Zone 3 is a DMZ I want to completely isolate from Zone 2, but still grant Inet access (game systems, webserver)

I am tyring to figure out how to do this in a cost effective manner.
I used to have a PC with a dedicated NIC for each zone running m0n0wall and it was pretty straight forward.

Now all I have is the Asus N66u. I have not found a way to isolate DMZ sever(s) (zone3) from other lan ports (Zone 2). (DDWRT allows this but would but I loose HW acceleration.)

So I was reading an article on the homepage that talked about dropping a smart switch behind the router then implement VLANs seperating zones 2 and3. However, thats less than cost effective (another $200)


Is there a more cost effective way to do this?