How many pairs of training underpants should I get?

My daughter on a daily basis will either tell me she has gone, tell me she has to go but refuses to sit in the potty and/or refuses to let me put a fresh diaper on her. (She prefers no diaper at all.)
I'm taking these as signs she's ready for the next step in the potty evolution.
My husband thinks letting her run free sans underpants for three days to get her to potty is all kinds of disgusting so the next best thing I think is to try training underpants.
So far everything I have read says not to spend too much money and stick with Gerber's. I guess my question is just how many pairs should I buy initially?
Also, since DH thinks toddlers naturally fall asleep on their own and learn to use the potty naturally, I'm gathering I'm going to be doing the brunt of this and DH may not be willing to deal with the training pants. Because of such, do you think having her wear training pants when it's just us and diapers when she's with daddy or long trips going to confuse and make things harder? Thoughts?
Thanks.
Post script: I broached the subject of underpants and DH responded that I'm jumping the gun and until she learns that the potty is wear she pees and poops, that she should stick with diapers. I'm not sure how he thinks she's going to realize this. He thinks that I may have harmed the potty training and caused her to regress because around 18 months, I would bring her to the potty in the morning and let her sit on her potty while I went to the potty. Back then she peed 50% of the time in the potty. I never pushed her but just allowed her to sit on it sans diaper while I was in the bathroom freshing up. In any case, I'm on my own on this.

There are lots of threads on PTing, so you should search for some of the old ones. People give pretty good advice! We loved the Hanna Andersson training unders SO much more than the Gerbers we were handed down. We made do with 6 pairs, but 9 would be more comfortable. They've been through 2 DC and look new still.

Thanks WatchingThemGrow!

Ditto watchingthemgrow. We had 6 pairs and it was fine. 9 might have been better but we made do with 6. We had the Hanna training unders as well.

Another Hanna training unders fan here. We had 9 pairs, but I think 6 would have been fine. My DH does laundry frequently :). They've held up well even through DH's harsh laudering - bleach, etc. My DD also quickly transitioned to regular Hanna unders, so that's another reason I thin 6 would have been enough. After she stopped wearing pullups to bed, we started using them at night and to this day those are still the panties/unders that she pulls out to put on with her jammies. She calls then her nighttime panties now.

We have 3 pairs of HA trainers and about 9 pairs of cheap hanes unders. We waited til DSs were closer to 3 years old so esp since boys train later we are told so 3 pairs were fine. Good luck!!
/hillary

Training unders we have 9-10, some HA, and some Gerber. Regular underwear, possibly 20 pairs. (DS still has little accidents where he waits too long to get to the potty to pee and wets a bit. So he still changes underwear a few times a day some days.)