How much you go depends on your menstrual circumstances. First year and change of marriage, when we weren't conceiving, I went every month. Since pregnancies started coming I haven't had many periods, so went post-miscarriages, post-partum, and whenever my periods started showing up again with all this nursing and tandem nursing business.
Yes, DH goes to the mikva. Regularly. As often as possible. At least every Friday (erev Shabbos) and before holidays, etc. That's at a minimum. Many other Orthodox men do that regularly, too.
Mikva is not just for taharas ha'mishpakha. Remembering the night my rebbe z'l passed away, I was still single and hadn't been to the mikva ever, so many of the khevre went to the mikva before being shomrei the guf ("guarding" the body), and the mikva lady was cool with whoever showed up (despite the ring-checking rumor) ... but I didn't do it because I also hate swimming and going under the water so just couldn't bring myself to do it if I didn't absolutely have to. Sigh.
The cost thing, agreeing with mom2seven. They've got to pay for the facilities and their upkeep and the laundry (lots of towels and bathrobes, right?) and supplies (soap, shampoo, nail polish remover, q-tips, etc., etc., etc.) but I've never ever heard of anyone being turned away for money issues.
This is contrasted, BTW, with men's mikvas, where some mikva'ot (in Israel, anyway) have turnstiles that you have to pay to even enter the facility.
Peppermint, going to the mikva is seven days after the cessation of menstruation. When you ovulate doesn't figure into the thing, unless there are fertility issues and a halakhic decision is made regarding the timing of immersion. But the rebbetzins on board could answer that better than I. By far.