I have been on Medicare for almost 2 years now. I am on low dose Tasigna - 150 mg once per day. My starting dose was 300 mg twice per day, so I'm on 25% of starting dose.
Go to the Medicare.gov website and make sure you enroll on time - there are significant penalties for not enrolling on time. Prior to enrolling you can use the Medicare.gov find a plan feature to review prescription plan options and premiums and drug costs. Use this link and then follow the prompts:
Medicare part D (Rx coverage) is free unless your income is high enough to require payment of a IRMAA, but you have to enroll in a Medicare Rx prescription drug plan and that is not free. I have the AARP MedicareRx Walgreen's, which costs $34.20 per month. There are cheaper premiums, but I use Walgreen's because their specialty pharmacy (the regular pharmacies don't stock this medicine) will ship my medicine to the local Walgreen's store and then they call me to go pick it up - much better than having UPS deliver to your house because you don't know when it's going to arrive and you worry all day long about $$$$$ of medicine sitting on your front porch. Also, if I'm away from home and need my Rx, they will ship it to a different Walgreen's store if I want.
The Medicare Rx coverage is phased - deductible, then co-pay, then "donut hole", then catastrophic. On 50 mg Sprycel you will hit catastrophic in month 2. My total annual out of pocket Tasigna costs this year will be $4,515 plus annual premium of $410, so right about $5,000. If I was on full dose, out of pocket drug cost would be $11,175 plus annual premium of $410, so close to $12,000. Not cheap by any means and a lot more then the $1,200 you are paying now. The website calculates all this for you and lets you compare plans, so it is pretty nifty in that regard.