Maybe if you talk about how little monetary difference his NOT going would make (he'd still have to eat, etc.), he might reconsider.
Also, maybe go look at mousesavers ( a website, just add the dot com) and look at WDW discounts and click on that - there are lists of ways to save money while at Disney.
Also, have you gotten the new codes for the new WDW packages (also on Mousesavers)? I did one a couple of months ago on an existing ressie and ended up saving $100 (that's about 1/2 an adult park ticket)
Rebooking is another option - are you going when prices are really high?
I would not want to go without him - it could be he is just suffering "sticker shock" with the final payment coming up.
Disney Visa has no interest no payment for 6 months on
Disney vacations. We just made our final "payment" this week, but we don't have to actually start paying till April. Gives us time to earn some more money, use some of our Christmas money, etc
Just some ideas - don't try to force it, but maybe if he could see there are some ways of making the trip more affordable, that might help.
Here's a prayer and a little pixie dust that things work out