I realize that my situation is most likely in the minority here, but this is what happened to me:
During my pregnancy with HG, I had Medica insurance. I live in Minnesota. Under my insurance policey, my "pre-natal" care was covered at 100%--no co-pays, no deductibles, nothing. Then I was hospitalized for 2 weeks (bills totalling over $56,000 for the stay alone), got a PICC line, TPN, lipids, zofran pump, Benadryl, and home care visits by an OB nurse three times a week (I am allergic to tape and the adhesive that was holding my PICC line in place, so the dressing had to be changed and repositioned to a different angle often).
The Zofran cassettes that went into my pump cost $1,300. That cassette lasted 42 hours, just under two days. I was on those 24/7 from my second month of pregnancy to my 7th. My co-pay for hospital visists, etc was 10%, which meant I would have to pay $130 for every 2 days I was on Zofran--5 months worth! Not to mention the home visits, supplies, TPN, lipids, etc.
I called my insurance company when I finally got rid of what I called my "octopus lines" and asked if I was going to get one huge bill all at once, or if they would allow me to make payment plans. Their response was: "You're not going to get a bill. It's all covered at 100%."
I didn't think he understood me right--I told him I knew my office visits were covered, but what about the rest? He again responded that it was ALL covered under pre-natal care. The hospital, meds, PICC line, EVERYTHING.
I started crying to the point my husband thought I had just received some awful news on the phone. I felt like I had won the lottery. I know not all insurance companies will cover things like that (my friend's insurance company wouldn't cover zofran for her at all because of the price).
And this may sound like really backwards advice, and it won't work for everyone, but if you can, get some sort of job in healthcare--as a secretary, nursing assistant, etc. (I was an NA.) Even with the...ahem..smells

, people will give you a free pass on those patients when they know you have HG. And you will have excellent insurance coverage. And people are very understanding that you need to take a lot of bathroom breaks and sit down a lot. Healthcare is one of the most understanding fields when you're suffering from HG.
By the way, pregnancy (and anything related to pregnancy) IS NOT a pre-existing condition when starting a new job and insurance. At least it's not here in MN. Best of luck to you!