Is a low cost router secure ?

Before the out break of Blaster virus, I am wondering whether a low cost router from LinkSys,SMC,Dlink,Netgear etc are secure enough ?
A security guru told me that those are toys in compare to some much more expensive real firewall programs or routers from CISCO. No one want to be false secure.
My question is are those consummer grade routers with NAT/SPI firewall secure ?
Generally speaking, Are they hackable ?
I assume all router will not open any port except we set it open for services.
If we keep all un-necessary ports close, Are those computers behind this router should not be vulnerable to hacking or security bugs ?
Any idea and comment…