How many concurrent users talking over links as an average?
40-50
What applications/protocols will be using links?
NetBIOS, FTP, File Sharing, Telnet, WSUS Servers, Symantec Servers, ICMP, all standard Server <-> Client Domain Traffic
VPN overhead might chew up more avail bandwidth than you want.
I was thinking of (3) Fortinet 80c hardware devices at each of the 3 gateways. Using IPSec VPN. The VPN overhead is what I'm concerned with.
Do you have budget? Do your policies dictate a commercial solution with support contracts?
Not much of a budget to speak of. A $2000 solution would require effort to get approved. No dictated solution to speak of.