We were able to talk them down on a last minute deal. If they aren't willing to negotiate with you, a 5-year customer, I would move on. Like others mentioned there are several other seals. Maybe you could get an estimate from one of the other seals and bring that to McAfee saying you'll take your business elsewhere if they don't come down in price.
Truthfully we picked up the seal mainly because our major competitors were. I was always iffy about seals actually boosting conversion rates... especially the hype sales staff will put behind them. Our conversion rate is up since installing the seal in 2011 but there are many reasons for this besides a security seal.