Firewall for 10MBit Line

Or as an alternative you can look into pfsense or m0n0wall for this which are bsd based firewall solutions or for a linux flavor your can try smoothwall or ipcop. A fun to play with alternative to these could be untangle. Untangle is similar to a sonicwall or watchguard device. These are highly affordable because the software is free and all you will be buying is the hardware, however there is a downside and that downside is dependant on how much you know about networking and firewalls.

http://m0n0.ch/wall/
http://www.pfsense.com/
http://www.smoothwall.org/
http://www.ipcop.org/
http://www.untangle.com/

If you were interested in the Cisco Option, I'd go with something out of the Cisco ASA 5500 series, the based 5505 can do 150mbps of throughput and it would be the cheapest one.
http://www.cisco.com/web/solutions/smb/products/security/asa_5500_series_adaptive_security_appliances.html#~models