A PIX 501 (ten user license) would probably cover your needs.
It supports VPN as well.
Another option would be to take the 1760 off-line and substitute something like an 870 series ISR.
The ISR will give you more processing power, and the software can handle IOS firewall (same / better functionality as the PIX), VPN, even wireless. The ISR can also give you Intrusion Detection (IDS) and / or Intrusion Prevention.
The ISR option will cost you more, but may give you a better suite of options down the road.
Good Luck
Scott