I used to be an air hog with similar bottom time issues; to this day I like big tanks when I can get them. Of course, experience, ease in the water, learning to relax/calm down, maybe learning you're overweighted and how to get by with less lead, these things can help get your gas consumption rate down. But in the mean time, big tanks rock.
Judging from
Dive With Martin's website, for a small upcharge they can provide 100-cf tanks.
Do you have your own gear or need a wetsuit? From that same web page for Dive With Martin:
"
- All prices include FREE rental gear, including BCD, regulator/gauges, fins and mask (based on availability)
- Wetsuits (3 mm shorty), dive computers and dive lights are available for rent on a daily basis"
If you plan to rent gear, that might impact the cost difference between the op.s.
I'm not weighing in on who to pick, just pointing out some publically available details that might interest you.
Richard.