Well, you have a hell of a lot more panel experience than me, since my first one ever is at the end of this month... and it's not like they approached us about doing one, I started bugging them about it early on and we'd already paid to be exhibitors.
From people I've talked to, sometimes you might at least be able to get a guest badge if someone who already has a panel there wants to have you be part of the panel... so maybe you could find out which of your friends and contacts are going to be in the programming and offer your services as a moderator?
Also, there's a certain amount of communication between convention staffers as well, so if you're in with "Convention X", maybe they'd put in the good word for you to "Convention Y". I don't think it matters what kind of business you're in, a good referral from a trusted source is worth its weight in gold.
Just thoughts. I figure they don't comp travel expenses except with people that are very established, but you might at least be able to attend the Con for free. Heck, my wife and I had only been doing our comic for about six months and San Diego approved our Professional applications, which is going to save us $600 over the course of the next few years.