No, after you qualify for Medicare you will no longer be eligible for an exchange plan. It's a shock to many.

Part A will be free.
Part B will be $124.

Your next decision needs to be if you want an Advantage Plan or a Supplement. Advantage Plans often cover your drugs, so you won't need to purchase Part D coverage. Some plans are free, some will cost a few hundred dollars. They are often HMO plans, with choices like Kaiser. Each state has different options. You can meet with a SHIP counselor in your state and they will advise you for free. Some people are very happy with their Advantage plans and some people are not...

A Supplement will give you much more flexibility and will cover your 20% deductibles. You'll still need to choose a Part D Drug Plan. By entering the drugs you use on the Medicare site, it'll give you prices for Advantage Plans and Part D plans and drug costs. You should call and confirm this info with any company you're considering, because they sometimes really won't pay for drugs when the Medicare website says they will.

If you don't choose a Supplement while you're eligible you're unlikely to find a plan that will accept you until you reach retirement age. There is more flexibility in switching to an Advantage plan later. You must check your Part D plans and drug copays every year if you have multiple Rx's because prices change significantly. If you choose an Advantage Plan, you should run those numbers as well.

My costs:

Part B: $104
Part D: $25
Supplement: $320
Drug co-pays: $120

I don't qualify for extra help and have an excellent Supplement. Supplement Plans use the alphabet from A-N. G and H are often exceptional and will have no deductible, and therefore will generally be the most expensive--sometimes lesser coverage costs more, so be careful. A SHIP counselor will probably be able to give you quotes and the best rated companies. My plan is through Mutual of Omaha. AARP uses United Healthcare, but in some states there are age restrictions.

So, IMO, the info you received was likely based on you paying for Part B, Part D, a Supplement, and drug copays. And yes, it will be substantially more expensive than what you have been. If it's any consolation, those prices were likely artificially low and won't continue...