OT - Vet visit for mice

Yes, I know this is a cat group but I know some of you have pet mice and/or
rats too so I'll throw my question out anywhere. Ignore if you want.

I'm a little disappointed in my vet today for what she charged me for
examining my 2 mice and prescribing Ivermectin, but no matter. Can't let
these little guys suffer if there are parasites. It just makes me sad that
people who will resist paying that much for a vet visit just won't do it ...
period. $86 US later, here's what we did:

One of my girls has been itching a lot and over the weekend I noticed more
red bumps on her and she's lost some fur. The other one didn't seem
affected but I'm glad I brought both of them, as she has some bumps too.
Florescent light revealed no ringworm, so that's good. Vet said it could be
mites, lice or even the two of them biting each other causing the damage. We
talked and decided to proceed assuming parasites since they both have bumps
and are itchy. I don't think my vet treats such small patients often
because she was challenged with how much Ivermectin to dose and how best to
dilute it so that it could be put into a bottle, and measured in a syringe.
It's going to be tricky getting this into those tiny mouths in 10 days. Vet
did today's dose herself.

How have you guys managed this if you've needed to? Vet said it can also be
used like a spot-on but I'd prefer to get it in their mouths to make sure
they get it all. Also, how often should I clean the bedding out until we
start noticing improvement? Would two times per week fully replacing the
bedding be enough or would you do it more? I already threw out the nest
that they sleep in and they'll have to live with what can be cleaned easier
until this is under control

Thanks,
Cheryl

PS - vet said the smaller of the two had some old trauma to one of her rear
legs and her tail. She said she's positive she's not in pain now or she'd
be chewing her leg and/or tail and she isn't. But she does have more
difficulty moving as she can't grip with one of her hind feet. She does run
on the wheel but not as fast as her sister, and not as often. She gets
around ok and climbs so it isn't like she's paralyzed or anything, just
trauma. She's been slower than the other one ever since I got her. She
hasn't had any accidents here since I've had her. I suspect it was the child
that was the cause of them being given away in the first place. Not the
child's fault. A 5 year old is too young for parents to give such fragile
pets to unless they can supervise every second they spend together.