With patience, you can find a Cisco ASA-5505 on ebay for under $300.
It is a (relatively) old firewall but will do anything a home network would need and then some.
You can upgrade RAM and Compact Flash for practically peanuts (standard computer parts).
You can install a free (for one year) SSL certificate from StartCOM.
By updating the ASA image on the router you can turn on PFS (Perfect Forward Secrecy
) and make NSA snooping on your communication a real PITA...
Two of the ASA's 8 ethernet ports have PoE that can be really useful when running IP phones...