Sunbelt Software's VIPRE will let you "switch" for $10/seat up to 500 seats (we need ~625) and claim they will buy out your current maintenance contract.
The biggest problem I have with McAfee is that it seems to be a total hog on every computer I've tried it on. Opening up IE 8 will cause EngineServer.exe to chew up 100% of the CPU and completely lock the computer up for as much as 30 seconds on the older PCs. Also, whenever there is an update pushed out by McAfee the computers slow to a total crawl. The settings that I define in our "management console" don't seem to do a damn think. For instance, I have the on-demand CPU time set to VERY LOW and it still uses 100% on every PC. I've posted on the SonicWALL and McAfee forums and have received no resolution. This happens on every single PC we have it installed on. Not only that, but AntiVirus XP 2010 and those other malware programs always seem to get installed undetected.
With VIPRE it's almost as fast as if there was no Anti-Virus installed at all. The detection rate is also supposedly top notch. It's a fairly new product though, having been out for less than 2 years - so I guess there is some risk involved there. From what I've been reading, the price is a lot cheaper than ESET and with the budget that I have to work with price will be the judge, jury, and executioner. We paid $12/seat for the McAfee we have now - but even that is too much. They should be paying us for all the extra power wasted from having the CPU always run so high!