Feel free to accuse me of whining.
Okay. Whiner.
I'll start by saying that my institution generally used to cover about 50% of all of my travel whether I did one, two, or eight conferences. Generally, they were happy to do this for solo papers at well-established international conferences, but I spoke at so many such conferences that travel was a fairly significant monetary burden.
Obviously, you should apply for more grants (which is something I did).
You could always tell your spouse to find a job, any job, or barring that, you could find a spouse and then tell your spouse to get a job, any job. Then you could use your spouse's income to indulge yourself in conference travel, or barring that, you could examine your family's habits... do you go to the movies, go to restaurants, go on holiday? If so, cancel these activities to pay for conference travel. While I was making the push to tenure and promotion, the entire family made sacrifices to ensure that my bid worked, but then again, my spouse worked.
Or you could obtain a stack of credit cards and go heavily into debt (which is also something I did) in order to speak at a lot of conferences in order to increase your profile so that you could get early tenure and promotion. Oh but you are tenured, so why don't you do what I do now, which is to cut your conference travel in half? I only do three disciplinary conferences per year now.
And since you're now a permanent fixture at your university, why not start to focus on conferences that will help your institution? You know, AAC&U, WAC/WIC, Accreditation, Honors, larger administrative concerns like that? If you deliver papers at those sorts of things, your institution will probably pay the entire bill, not just a small portion. I go to three or four such things a year, and all of my expenses are always covered, in some cases, by the conference as part of some institutional membership or another. The publication opportunities that come from these sorts of conferences are also pretty real. It's good to show that you're interested in the nuts and bolts of an institution, especially if a future promotion to full professor will be based on a vote by some institution-wide committee of the most senior faculty. Where I work, they want to see evidence of an international scholarly reputation, but also evidence that you're good for the institution itself, that you've taken an active interest in its smooth operation.